The apex of the heart is pointed and more solid than the rest of the organ. It lies against the breast, and entirely in the anterior part of the body, in order to prevent that region from getting chilled. For in all animals there is comparatively little flesh over the breast, whereas there is a more abundant covering of that [5] substance on the posterior surface, so that the heat has in the back a sufficient amount of protection. In all animals but man the heart is placed in the centre of the pectoral region; but in man it inclines a little towards the left, so that it may counterbalance the chilliness of that side. For the left side is colder in man than in [10] any other animal. It has been stated earlier that even in fishes the heart holds the same position as in other animals; and the reason has been given why it appears not to do so. The apex of the heart, it is true, is in them turned towards the head, but this in fishes is the front aspect, for it is the direction in which their motion occurs.

The heart again is abundantly supplied with sinews, as might reasonably be expected. For the motions of the body commence from the heart, and are brought [15] about by traction and relaxation. The heart therefore, which, as already said, is as it were a living creature inside its possessor, requires some such subservient and strengthening parts.

In no animals does the heart contain a bone, certainly in none of those that we have ourselves inspected, with the exception of the horse and a certain kind of ox. In these the heart, owing to its large bulk, is provided with a bone as a support; just as [20] the bones serve as supports for the body generally.

In animals of great size the heart has three cavities; in smaller animals it has two; and in all has at least one, for, as already stated, there must be some place in the heart to serve as a receptacle for the first blood; which, as has been mentioned more than once, is formed in this organ. But inasmuch as the main blood-vessels are [25] two in number, namely the so-called great vessel and the aorta, each of which is the origin of other vessels; inasmuch, moreover, as these two vessels present differences, hereafter to be discussed, when compared with each other, it is of advantage that they also shall themselves have distinct origins. This advantage will be obtained if each side have its own blood, and the blood of one side be kept separate from that of [30] the other. For this reason the heart, whenever it is possible, has two receptacles. And this possibility exists in the case of large animals, for in them the heart too is of large size. Again it is still better that there shall be three cavities, so that the middle and odd one may serve as a source common to both sides. But this requires the heart to be of greater magnitude, so that it is only in the largest hearts that there are three [35] cavities.

Of these three cavities it is the right that has the most abundant and the hottest [667a1] blood, and this explains why the limbs also on the right side of the body are warmer than those on the left. The left cavity has the least blood of all, and the coldest; while in the middle cavity the blood, as regards quantity and heat, is intermediate to the other two, being however of purer quality than either. For it behoves the principal part to be as tranquil as possible, and this tranquillity can be ensured by the blood [5] being pure, and of moderate amount and warmth.

In the heart of animals there is also a kind of joint-like division, something like the sutures of the skull. This is not, however, attributable to the heart being formed by the union of several parts into a compound whole, but is rather, as already said, the result of a joint-like division. These jointings are most distinct in animals of keen [10] sensibility, and less so in those that are of duller feeling, in swine for instance. Different hearts differ also from each other in their sizes, and in their degrees of firmness; and these differences somehow extend their influence to the temperaments of the animals. For in animals of low sensibility the heart is hard and dense in [15] texture, while it is softer in such as are endowed with keener feeling. So also when the heart is of large size the animal is timorous, while it is more courageous if the organ be smaller and of moderate bulk. For in the former the bodily affection which results from terror already pre-exists; for the bulk of the heart is out of all proportion to the animal’s heat, which being small is reduced to insignificance in the large space, and thus the blood is made colder than it would otherwise be.

[20] The heart is of large size in the hare, the deer, the mouse, the hyena, the ass, the leopard, the weasel, and in pretty nearly all other animals that either are manifestly timorous, or betray their cowardice by their spitefulness.

What has been said of the heart as a whole is no less true of its cavities and of the blood-vessels; these also if of large size being cold. For just as a fire of equal size [25] gives less heat in a large room than in a small one, so also does the heat in the present case; for the vessels and the cavities are receptacles. Moreover, all hot bodies are cooled by motions external to themselves, and the more spacious the cavities and vessels are, the greater the amount of breath they contain, and the more [30] potent its action. Thus it is that no animal that has large cavities in its heart, or large blood-vessels, is ever fat, the vessels being indistinct and the cavities small in all or most fat animals.

The heart again is the only one of the viscera, and indeed the only part of the body, that is unable to tolerate any serious affection. This is but what might reasonably be expected. For, if the primary part be diseased, there is nothing from [667b1] which the other parts which depend upon it can derive succour. A proof that the heart is thus unable to tolerate any affection is furnished by the fact that in no sacrificial victim has it ever been seen to be affected with those diseases that are observable in the other viscera. For the kidneys are frequently found to be full of [5] stones, and growths, and small abscesses, as also are the liver, the lung, and more than all the spleen. There are also many other conditions which are seen to occur in these parts, those which are least liable to such being the portion of the lung which is close to the windpipe, and the portion of the liver which lies about the junction with [10] the great blood-vessel. This again admits of a rational explanation. For it is in these parts that they are most closely in communion with the heart. On the other hand, when animals die not by sacrifice but from disease, and from affections such as are mentioned above, they are found on dissection to have morbid affections of the heart.

Thus much of the heart, its nature, and the end and cause of its existence in such animals as have it.

[15] 5 · In due sequence we have next to discuss the blood-vessels, that is to say the great vessel and the aorta. For it is into these two that the blood first passes when it quits the heart; and all the other vessels are but offshoots from them. Now that these vessels exist on account of the blood has already been stated. For every fluid requires a receptacle, and in the case of the blood the vessels are that [20] receptacle. Let us now explain why these vessels are two, and why they spring from one single source, and extend throughout the whole body.

The reason, then, why these two vessels coalesce into one centre, and spring from one source, is that the sensory soul is in all animals actually one, so that the part in which it primarily abides must also be one. In sanguineous animals this oneness is not only actual but potential, whereas in some bloodless animals it is only [25] actual. Hence in the self-same place must necessarily be the source of heat; and this is the cause of the warmth and fluidity of the blood. Thus, then, the oneness of the part in which is lodged the prime source of sensation and of heat explains the oneness of the source in which the blood originates; and this, again, explains why [30] the blood-vessels have one common starting-point.

The vessels are two because the body of every sanguineous animal that is capable of locomotion is bilateral; for in all such animals there is a distinguishable before and behind, a right and left, an above and below. Now as the front is more honourable and of higher supremacy than the hinder aspect, so also and in like degree is the great vessel superior to the aorta. For the great vessel is placed in front, [668a1] while the aorta is behind; the former again is plainly visible in all sanguineous animals, while the latter is in some indistinct and in some not discernible at all.

Lastly, the reason for the vessels being distributed throughout the entire body is that in them, or in parts analogous to them, is contained the blood, or the fluid which in bloodless animals takes the place of blood, and that this is the material from which the whole body is made. Now as to the manner in which animals are [5] nourished, and as to the source from which they obtain nutriment and as to the way in which they absorb this from the stomach, these are matters which may be more suitably considered and explained in the treatise on Generation. [But inasmuch as the parts are, as already said, formed out of the blood, it is but rational that the flow [10] of the blood should extend, as it does, throughout the whole of the body. For since each part is formed of blood, each must have blood all about it.]11

To give an illustration of this. The water-courses in gardens are so constructed as to distribute water from one single source or fount into numerous channels, which [15] convey it to all parts; and, again, in house-building stones are thrown down along the whole ground-plan of the foundation walls; because the garden-plants in the one case take their growth from water, and the foundation walls in the other are built out of the stones. Now just after the same fashion has nature laid down channels for [20] the conveyance of the blood throughout the whole body, because this blood is the material out of which the whole fabric is made. This becomes very evident in bodies that have undergone great emaciation. For in such there is nothing to be seen but the blood-vessels; just as when fig-leaves or vine-leaves or the like have dried up, [25] there is nothing left of them but their vessels. The explanation of this is that the blood, or fluid which takes its place, is potentially body and flesh, or substance analogous to flesh. Now just as in irrigation the largest dykes are permanent, while the smallest are soon filled up with mud and disappear, again to become visible [30] when the deposit of mud ceases; so also do the largest blood-vessels remain permanently open, while the smallest are converted actually into flesh, though potentially they are no whit less vessels than before. This too explains why, so long as the flesh of an animal is in its integrity, blood will flow from any part of it whatsoever that is cut. Now there can be no blood, unless there be a blood-vessel, and yet no vessel is visible—just as the dykes for irrigation are invisible until they [668b1] have been cleared of mud.

As the blood-vessels advance, they become gradually smaller and smaller, until at last their tubes are too fine to admit the blood. This fluid can therefore no longer find its way through them, though they still give passage to the residue of the moist [5] humour which we call sweat; and especially so when the body is heated, and the mouths of the small vessels are dilated. Instances, indeed, are not unknown of persons who in consequence of a bad general condition have secreted sweat that resembled blood, their body having become loose and flabby, and their blood watery, owing to the heat in the small vessels having been too scanty for its [10] concoction. For, as was before said, every compound of earth and water—and both nutriment and blood are such—becomes thicker from concoction. The inability of the heat to effect concoction may be due either to its being absolutely small in amount, or to the quantity of food, when this has been taken in excess and relative to [15] which it is small. This excess again may be of two kinds, either quantitative or qualitative; for all substances are not equally amenable to concoction.

The widest passages in the body are of all parts the most liable to haemorrhage; so that bleeding occurs not infrequently from the nostrils, the gums, and the fundament, occasionally also from the mouth. Such haemorrhages are of a painless kind, and not violent as are those from the windpipe.

[20] The great vessel and the aorta, which above lie somewhat apart, lower down exchange positions, and by so doing give compactness to the body. For when they reach the point where the legs diverge, they each split into two, and the great vessel passes from the front to the rear, and the aorta from the rear to the front. By this [25] they contribute to the unity of the whole fabric. For as in plaited work the parts hold more firmly together, so also by the interchange of position between the blood-vessels are the anterior and posterior parts of the body more closely knit together. A similar exchange of position occurs also in the upper part of the body, between the vessels that have issued from the heart. The details however of the mutual relations [30] of the different vessels must be looked for in the Dissections and the History of Animals.

So much, then, as concerns the heart and the blood-vessels. We must now pass on to the other viscera and apply the same method of inquiry to them.

6 · The lung, then, is an organ found in all the animals of a certain class, because they live on land. For there must of necessity be some means or other of tempering the heat of the body; and in sanguineous animals, as they are of an especially hot nature, the cooling agency must be external, whereas in the bloodless [669a1] kinds the innate spirit is sufficient of itself for the purpose. The external cooling agent must be either air or water. In fishes the agent is water. Fishes therefore never [5] have a lung, but have gills in its place, as was stated in the treatise on Respiration. But animals that breathe are cooled by air. These therefore are all provided with a lung.

All land animals breathe, and even some water animals, such as the whale, the dolphin, and all the spouting Cetacea. For many animals are ambivalent: some that [10] are terrestrial and that inspire air being nevertheless of such a bodily constitution that they abide for the most time in the water; and some that are aquatic partaking so largely of the land character, that respiration constitutes for them the limiting condition of life.

The organ of respiration is the lung. This derives its motion from the heart; but [15] it is its own large size and spongy texture that affords amplitude of space for the entrance of the breath. For when the lung rises up the breath streams in, and is again expelled when the lung collapses. It has been said that the lung exists as a provision to meet the jumping of the heart. But this is out of the question. For man is practically the only animal whose heart presents this phenomenon of jumping, [20] inasmuch as he alone is influenced by hope and anticipation of the future. Moreover, in most animals it is separated from the lung by a considerable interval and lies above it, so that the lung can contribute nothing to mitigate any jumping of the heart.

The lung differs much in different animals. For in some it is of large size and contains blood; while in others it is smaller and of spongy texture. In the vivipara it [25] is large and rich in blood, because of their natural heat; while in the ovipara it is small and dry but capable of expanding to a vast extent when inflated. Among terrestrial animals, the oviparous quadrupeds, such as lizards, tortoises, and the [30] like, have this kind of lung; and, among inhabitants of the air, the animals known as birds. For in all these the lung is spongy, and like foam. For foam contracts from a large mass to a small when it runs together, and the lung of these animals is small and membraneous. In this too lies the explanation of the fact that these animals are little liable to thirst and drink but sparingly, and that they are able to remain for a [35] considerable time under water. For, inasmuch as they have but little heat, the very motion of the lung, airlike and void, suffices by itself to cool them for a considerable [669b1] period.

These animals, speaking generally, are also distinguished from others by their smaller bulk. For heat promotes growth, and abundance of blood is an indication of heat. Heat, again, tends to make the body erect; and thus it is that man is the most [5] erect of animals, and the vivipara more erect than other quadrupeds. For no viviparous animal, be it footless or be it possessed of feet, is so given to creep into holes.

The lung, then, exists in general for respiration; but in one order of animals it is bloodless and has the structure described above, to suit the special requirements. There is, however, no one term to denote all animals that have a lung; no [10] designation, that is, like the term bird, applicable to the whole of a certain class. Yet the possession of a lung is a part of their substance, just as much as the presence of certain characters constitutes the essence of a bird.

7 · Of the viscera some appear to be single, as the heart and lung; others to be [15] double, as the kidneys; while of a third kind it is doubtful in which class they should be reckoned. For the liver and the spleen would seem to be ambivalent. For they may be regarded either as constituting each a single organ, or as a pair of organs resembling each other in character.

In reality, however, all the organs are double. The reason for this is that the body itself is double, consisting of two halves, which are however combined together [20] under a single origin. For there is an upper and a lower half, a front and a rear, a right side and a left.

This explains why it is that even the brain and the several organs of sense tend in all animals to consist of two parts; and the same explanation applies to the heart with its cavities. The lung again in Ovipara is divided to such an extent that these [25] animals look as though they had actually two lungs. As to the kidneys, no one can overlook their double character. But when we come to the liver and the spleen, any one might fairly be in doubt. The reason for this is, that, in animals that necessarily have a spleen, this organ is such that it might be taken for a kind of bastard liver; while in those in which a spleen is not an actual necessity but is merely present, as it [30] were, by way of token, in an extremely minute form, the liver plainly consists of two parts; of which the larger tends to lie on the right side and the smaller on the left. Not but what there are some even of the Ovipara in which this condition is comparatively indistinctly marked; while, on the other hand, there are some Vivipara in which the liver is manifestly divided into two parts. Examples of such division are furnished by the hares of certain regions, which have the appearance of having two livers, and by the selachia and some other fishes.

[670a1] It is the position of the liver on the right side of the body that is the main cause for the formation of the spleen; the existence of which thus becomes to a certain extent a matter of necessity in all animals, though not of very stringent necessity.

The reason, then, why the viscera are bilateral is, as we have said, that there [5] are two sides to the body, a right and a left. For each of these sides aims at similarity with the other, and so likewise do their several viscera; and as the sides, though dual, are knit together into unity, so also is it with each of the viscera.

Those viscera which lie below the diaphragm exist one and all on account of [10] the blood-vessels; serving as a bond, by which these vessels, while floating freely, are yet held in connexion with the body. For the vessels give off branches which run to the body through the outstretched structures, like so many anchor-lines. The great vessel sends such branches to the liver and the spleen; and these viscera—the liver [15] and spleen on either side with the kidneys behind—attach the great vessel to the body with the firmness of nails. The aorta sends similar branches to each kidney.

[20] These viscera, then, contribute in this manner to the animal body. The liver and spleen assist, moreover, in the concoction of the food; for both are of a hot character, owing to the blood which they contain. The kidneys, on the other hand, take part in the separation of the excretion which flows into the bladder.

The heart then and the liver are essential constituents of every animal; the liver that it may effect concoction, the heart that it may lodge the central source of heat. For some part or other there must be which, like a hearth, shall hold the kindling [25] fire; and this part must be well protected, seeing that it is, as it were, the citadel of the body.

All sanguineous animals, then, need these two parts; and this explains why these two viscera are found in them all. In such of them, however, as breathe, there is also a third, namely the lung. The spleen, in those animals that have it, is only [30] present of necessity in the same sense as the excretions of the belly and of the bladder are necessary, in the sense, that is, of being a concomitant. Therefore it is that in some animals the spleen is but scantily developed as regards size. This, for instance, is the case in such feathered animals as have a hot stomach. Such are the pigeon, the hawk, and the kite. It is the case also in oviparous quadrupeds, where the [670b1] spleen is excessively minute, and in many of the scaly fishes. These same animals are also without a bladder, because the loose texture of their flesh allows the residual fluid to pass through and to be applied to the formation of feathers and scales. For the spleen attracts the residual humours from the stomach, and owing to [5] its bloodlike character is enabled to assist in their concoction. Should, however, this residual fluid be too abundant, or the heat of the spleen be too scanty, the body becomes sickly from over-repletion with nutriment. Often, too, when the spleen is affected by disease, the belly becomes hard owing to the reflux into it of the fluid; just as happens to those who form too much urine, for they also are liable to a [10] similar diversion of the fluids into the belly. But in those animals that have but little to excrete, such as birds and fishes, the spleen is never large, and in some exists no more than by way of token. So also in the oviparous quadrupeds it is small, compact, and like a kidney. For their lung is spongy, and they drink but little, and such [15] residue as they have is applied to the growth of the body and the formation of scaly plates, just as in birds it is applied to the formation of feathers.

On the other hand, in such animals as have a bladder, and whose lung contains blood, the spleen is watery, both for the reason already mentioned, and also because the left side of the body is more watery and colder than the right. For each of two [20] contraries has been so placed as to go together with that which is akin to it in another pair of contraries. Thus right and left, hot and cold, are pairs of contraries; and they are in the same column as one another, after the manner described.

The kidneys when they are present exist not of actual necessity, but as matters of greater finish and perfection. For by their special character they are suited to serve in the excretion of the fluid which collects in the bladder. In animals therefore [25] where this fluid is very abundantly formed, their presence enables the bladder to perform better its proper office.

Since then both kidneys and bladder exist in animals for one and the same function, we must next treat of the bladder, though in so doing we disregard the due [30] order of succession in which the parts should be enumerated. For not a word has yet been said of the midriff, which is one of the parts that environ the viscera.

8 · It is not every animal that has a bladder; those only being apparently [671a1] intended by nature to have one, whose lung contains blood. To such it was but reasonable that she should give this part. For the superabundance in their lung of its natural constituents causes them to be the thirstiest of animals, and makes them require a more than ordinary quantity not merely of solid but also of liquid nutriment. This increased consumption necessarily entails the production of an [5] increased amount of residue; which thus becomes too abundant to be concocted by the stomach and excreted with its own residual matter. The residual fluid must therefore of necessity have a receptacle of its own; and thus all animals whose lung contains blood are provided with a bladder. Those animals, on the other hand, that are without a lung of this character, and that either drink but sparingly owing to [10] their lung being of a spongy texture, or never imbibe fluid at all for drinking’s sake but only as nutriment, insects for instance and fishes, and that are moreover clad with feathers or scales or scaly plates—all these animals, owing to the small amount of fluid which they imbibe, and owing also to such residue as there may be being [15] converted into feathers and the like, are invariably without a bladder. The tortoises, which are comprised among animals with scaly plates, form the only exception; and this is merely due to the imperfect development of their natural conformation; the explanation of the matter being that in the sea-tortoises the lung is flesh-like and contains blood, resembling the lung of the ox, and that in the land-tortoises it is of disproportionately large size. Moreover, inasmuch as the covering which invests [20] them is dense and shell-like, so that the moisture cannot exhale through the porous flesh, as it does in birds and in snakes and other animals with scaly plates, such an amount of secretion is formed that some special part is required to receive and hold it. This then is the reason why these animals, alone of their kind, have a bladder, the [25] sea-tortoise a large one, the land-tortoises an extremely small one.

9 · What has been said of the bladder is equally true of the kidneys. For these also are wanting in all animals that are clad with feathers or with scales or with scale-like plates; the sea and land tortoises forming the only exception. In some of the birds, however, there are flattened kidney-like bodies, as though the flesh [30] allotted to the formation of the kidneys, unable to find one single place of sufficient size, had been scattered over several.

The fresh-water tortoise has neither bladder nor kidneys. For the softness of its shell allows of the ready transpiration of fluid; and for this reason neither of the organs mentioned exists in this animal. All other animals, however, whose lung [671b1] contains blood are, as before said, provided with kidneys. For nature uses these organs for two separate purposes, namely for the excretion of the residual fluid, and to subserve the blood-vessels, a channel leading to them from the great vessel.

In the centre of the kidney is a cavity of variable size. This is the case in all [5] animals, excepting the seal. The kidneys of this animal are more solid than those of any other, and resemble the kidneys of the ox. The human kidneys are also like those of the ox; being as it were made up of numerous small kidneys, and not presenting one unbroken surface like the kidneys of sheep and other quadrupeds. For this reason, should the kidneys of a man be once attacked by disease, the [10] malady is not easily expelled. For it is as though many kidneys were diseased and not merely one; which naturally enhances the difficulties of a cure.

The duct which runs to the kidney from the great vessel does not terminate in the central cavity, but is expended on the substance of the organ, so that there is no blood in the cavity, nor does any congeal there after death. A pair of stout ducts, [15] void of blood, run, one from the cavity of each kidney, to the bladder; and other ducts, strong and continuous, lead into the kidneys from the aorta. The purpose of this arrangement is to allow the superfluous fluid to pass from the blood-vessel into the kidney, and the resulting renal excretion to collect, by the percolation of the [20] fluid through the solid substance of the organ, in its centre, where as a general rule there is a cavity. (This by the way explains why the kidney is the most malodorous of all the viscera.) From the central cavity the fluid is discharged into the bladder by the ducts that have been mentioned, having already assumed in great degree the character of excremental residue. The bladder is as it were moored to the kidneys; [25] for, as already has been stated, it is attached to them by strong ducts. These then are the causes for which the kidneys exist, and such the functions of these organs.

In all animals that have kidneys, that on the right is placed higher than that on the left. For, inasmuch as motion commences from the right, and the organs on this [30] side are in consequence stronger than those on the left, they must all push upwards because of this motion in advance of their opposite fellows; indeed, men even raise the right eyebrow more than the left, and the former is more arched than the latter. The right kidney being thus drawn upwards is in all animals brought into contact with the liver; for the liver lies on the right side. [672a1]

Of all the viscera the kidneys are those that have the most fat. This is in the first place the result of necessity, because the kidneys are the parts through which the residual matters percolate. For the blood which is left behind after this excretion, being of pure quality, is of easy concoction, and the final result of thorough blood-concoction is lard and suet. For just as a certain amount of fire is [5] left in the ashes of solid substances after combustion, so also does a remnant of the heat that has been developed remain in fluids after concoction; and this is the reason why oily matter is light, and floats on the surface of other fluids. The fat is not formed in the kidneys themselves, the density of their substance forbidding this, but [10] is deposited about their external surface. It consists of lard or of suet, according as the animal’s fat is of the former or latter character. The difference between these two kinds of fat has already been set forth in other passages. The formation, then, of fat in the kidneys is the result of necessity; being, as explained, a consequence of the necessary conditions which accompany the possession of such organs. But at the [15] same time the fat is there to ensure the safety of the kidneys, and to maintain their natural heat. For placed, as these organs are, close to the surface, they require a greater supply of heat than other parts. For while the back is thickly covered with flesh, so as to form a shield for the heart and neighbouring viscera, the loins, in accordance with a rule that applies to all bendings, are destitute of flesh; and fat is therefore formed as a substitute for it, so that the kidneys may not be without [20] protection. The kidneys, moreover, by being fat are the better enabled to secrete and concoct their fluid; for fat is hot, and it is heat that effects concoction.

Such, then, are the reasons why the kidneys are fat. But in all animals the right kidney is less fat than its fellow. The reason for this is, that the parts on the right [25] side are naturally more dry and more suited for motion than those on the left. But motion is antagonistic to fat, for it tends to melt it.

Animals then, as a general rule, derive advantage from their kidneys being fat; and the fat is often very abundant and extends over the whole of these organs. But, should the like occur in the sheep, death ensues. Be its kidneys, however, as fat as [30] they may, they are never so fat but that some part, if not in both at any rate in the right one, is left free. The reason why sheep are the only animals that suffer in this manner, or suffer more than others, is that in animals whose fat is composed of lard this is of fluid consistency, so that there is not the same chance in their case of breath getting shut in and causing mischief. But it is to this that rot is due. And thus [35] even in men who suffer from kidney trouble, though it is beneficial to them to have fat kidneys, yet should these organs become over-fat, deadly pains ensue. As to [672b1] those animals whose fat consists of suet, in none is the suet so dense as in the sheep, neither is it nearly so abundant; for of all animals there is none in which the kidneys become so soon gorged with fat as in the sheep. Rot, then, is produced by the moisture and the breath getting shut up in the kidneys, and is a malady that carries [5] off sheep with great rapidity. For the disease forthwith reaches the heart, passing thither by the aorta and great vessel, the ducts which connect these with the kidneys being of unbroken continuity.

10 · We have now dealt with the heart and the lung, as also with the liver, [10] spleen, and kidneys. The latter are separated from the former by the midriff or, as some call it, the diaphragm. This divides off the heart and lung, and, as already said, is called the diaphragm in sanguineous animals, all of which have a midriff, just as they all have a heart and a liver. The reason is that the midriff serves to [15] divide the region of the heart from the region of the stomach, so that the centre wherein abides the sensory soul may be undisturbed, and not be overwhelmed, directly food is taken, by its up-steaming vapour and by the abundance of heat then superinduced. For it was to guard against this that nature made a division, [20] constructing the midriff as a kind of partition-wall and fence, and so separated the nobler from the less noble parts, in all cases where a separation of upper from lower is possible. For the upper part is the better and that for the sake of which the rest exists; while the lower part exists for the sake of the upper and constitutes the necessary element in the body, inasmuch as it is the recipient of the food.

[25] That portion of the midriff which is near the ribs is fleshier and stronger than the rest, but the central part has more of a membranous character; for this structure conduces best to its strength and its extensibility. Now that there are as it were outgrowths to prevent heat mounting up from below, is shown by what happens when, owing to their proximity to the stomach, they attract thence the hot and residual fluid. For when this occurs there ensues forthwith a marked disturbance of [30] intellect and sensation. It is indeed because of this that the midriff is called the diaphragm, as though it had some share in the process of thinking.12 In reality, however, it has no part whatsoever itself in the matter, but, lying in close proximity to organs that have, it makes the changes of intelligence evident. This too explains why its central part is thin—not only by necessity, inasmuch as those portions of the fleshy whole which lie nearest to the ribs must necessarily be fleshier than the rest, [35] but also in order to give it as small a proportion of humour as possible; for, had it been made of flesh throughout, it would have been more likely to attract and hold a [673a1] large amount of this. That heating of it affects sensation rapidly and in a notable manner is shown by the phenomena of laughing. For when men are tickled they are quickly set a-laughing, because the motion quickly reaches this part, and being heated but slightly it nevertheless manifestly so disturbs the mental action as to occasion movements that are contrary to the man’s intention. That man alone is affected by tickling is due firstly to the delicacy of his skin, and secondly to his being [5] the only animal that laughs. For to be tickled is to be set in laughter, the laughter being produced by such a motion as mentioned of the region of the armpit. [10]

It is said also that when men in battle are wounded anywhere near the midriff, they are seen to laugh, owing to the heat produced by the wound. This is asserted by more credible persons than those who tell the story of how a human head speaks after it is cut off. For so some assert, and even call in Homer to support them, representing [15] him as alluding to this when he wrote, ‘His head still speaking rolled into the dust’, instead of ‘The head of the speaker’.13 So fully was the possibility of such an occurrence accepted in Arcadia, that one of that country was actually brought to trial under the following circumstances. The priest of Zeus Hoplosmios had been murdered; but as yet it had not been ascertained who was the assassin; when certain persons asserted that they [20] had heard the murdered man’s head, which had been severed from the body, repeat several times the words, ‘Cercidas slew man on man’. Search was thereupon made and a man of those parts who bore the name of Cercidas hunted out and put upon his trial. But it is impossible that any one should utter a word when the windpipe is severed and no motion any longer derived from the lung. Moreover, among the barbarians, where heads are chopped off with great rapidity, nothing of the kind has ever yet occurred. [25] Why, again, does not the like occur in the case of other animals than man? [For the story about laughing when the midriff is wounded, is but what one would expect; for no animal but man ever laughs. So, too, there is nothing irrational in supposing that the trunk may run forwards to a certain distance after the head has been cut off; seeing that bloodless animals at any rate can live, and that for a considerable time, after decapitation, [30] as has been set forth and explained in other passages.]14

The purposes, then, for which the viscera severally exist have now been stated. It is of necessity upon the inner terminations of the vessels that they are developed; [673b1] for humour, and that of a bloody character, cannot but exude at these points, and it is of this, solidified and coagulated, that the substance of the viscera is formed. Thus they are of a bloody character, and in substance resemble each other while they differ from other parts.

11 · The viscera are enclosed each in a membrane. For they require some [5] covering to protect them from injury, and require, moreover, that this covering shall be light. To such requirements membrane is well adapted; for it is close in texture so as to form a good protection, destitute of flesh so as neither to attract humour nor retain it, and thin so as to be light and not add to the weight of the body. Of the membranes those are the stoutest and strongest which invest the heart and the [10] brain; as is but consistent with reason. For these are the parts which require most protection, seeing that they are the main governing powers of life, and that it is to governing powers that guard is due.

12 · Some animals have all the viscera that have been enumerated; others have only some of them. In what kind of animals this latter is the case, and what is the explanation, has already been stated. Moreover, the self-same viscera present [15] differences in different possessors. For the heart is not precisely alike in all animals that have one; nor, in fact, is any of the others. Thus the liver is in some animals split into several parts, while in others it is comparatively undivided. Such differences present themselves even among those sanguineous animals that are viviparous, but [20] are marked in fishes and in the oviparous quadrupeds, and this whether we compare them with each other or with the Vivipara. As for birds, their liver very nearly resembles that of the Vivipara; for in them, as in these, it is of a pure and blood-like colour. The reason for this is that the body in both these classes of animals admits of the freest exhalation and the amount of foul residual matter within is but small. [25] Hence it is that some of the Vivipara are without any gall-bladder at all. For the liver takes a large share in maintaining the purity of composition and the healthiness of the body. For these are conditions that depend finally upon the blood, and there is more blood in the liver than in any of the other viscera, the heart only excepted. On the other hand, the liver of oviparous quadrupeds and fishes inclines, as a rule, to a yellow hue, and there are even some of them in which it is entirely of [30] this bad colour, in accordance with the bad composition of their bodies generally. Such, for instance, is the case in the toad, the tortoise, and other similar animals.

The spleen in animals that have horns and cloven hoofs, such as the goat, the sheep, and the like, is of a rounded form; excepting when increased size has caused [674a1] some part of it to extend its growth longitudinally, as has happened in the case of the ox. On the other hand, it is elongated in all polydactylous animals. Such, for instance, is the case in the pig, in man, and in the dog. While in animals with solid hoofs it is of a form intermediate to these two and mixed, being broad in one part, narrow in another. Such, for example, is its shape in the horse, the mule, and the ass.

13 · The viscera differ from the flesh not only in the bulkiness of their [5] substance, but also in position; for they lie within the body, whereas the flesh is placed on the outside. The explanation of this is that these parts partake of the character of blood-vessels, and that while the former exist for the sake of the vessels, the latter cannot exist without them.

14 · Below the midriff lies the stomach, placed at the end of the oesophagus [10] when there is one, and in immediate contiguity with the mouth when the oesophagus is wanting. Continuous with this stomach is what is called the gut. These parts are present in animals, for reasons that are self-evident. For it is a matter of necessity that an animal shall receive the incoming food and discharge it when its moisture has been extracted. This residual matter, again, must not occupy [15] the same place as the yet unconcocted nutriment, and there must be a place in which they change. For there must be one receptacle for the ingoing food and another for the useless residue, and as there are separate times for these operations, so there must be distinct places. These, however, are matters which will be more suitably set forth when we come to deal with Generation and Nutrition. What we [20] have at present to consider are the variations presented by the stomach and its subsidiary parts. For neither in size nor in shape are these parts uniformly alike in all animals. Thus the stomach is single in all sanguineous and viviparous animals which are ambidentate. It is single therefore in all the polydactylous kinds, such as man, dog, lion, and the rest; in all the solid-hoofed animals also, such as horse, mule, [25] ass; and in all those which, like the pig, though their hoof is cloven, yet are ambidentate. When, however, an animal is of large size, and feeds on substances of so thorny and ligneous a character as to be difficult of concoction, it may in [30] consequence have several stomachs, as for instance is the case with the camel. A similar multiplicity of stomachs exists also in the horned animals; the reason being that horn-bearing animals are not ambidentate. The camel also, though it has no horns, is not ambidentate. The explanation of this is that it is more essential for the camel to have a multiple stomach than to have front teeth. Its stomach, then, is constructed like that of non-ambidentates, and its teeth match its stomach—for the [674b1] teeth in question would be of no service. Its food, moreover, being of a thorny character, and its tongue necessarily made of a fleshy substance, nature uses the earthy matter which is saved from the teeth to give hardness to the palate. The [5] camel ruminates like the horned animals, because its multiple stomach resembles theirs. For all animals that have horns, the sheep for instance, the ox, the goat, the deer, and the like, have several stomachs. For since the mouth, owing to its lack of [10] teeth, only imperfectly performs its office as regards the food, the stomachs receive the food one from the other in succession, the first taking the unreduced substances, the second the same when somewhat reduced, the third when reduction is complete, and the fourth when the whole has become a smooth pulp. Such is the reason why there is this multiplicity of parts and cavities in animals with such dentition. The names given to the several cavities are the paunch, the honey-comb bag, the [15] manyplies, and the reed. How these parts are related to each other, in position and in shape, must be looked for in the History of Animals and the Anatomies.

Birds also present variations in the part which acts as a recipient of the food for [20] the same reason. For here again it is because the mouth fails to perform its office—for birds have no teeth at all, nor any instrument whatsoever with which to bite up or grind down their food—it is because of this, that in some of them what is called the crop precedes the stomach and does the work of the mouth; while in others the oesophagus is either broad or a part of it bulges just before it enters the [25] stomach, so as to form a preparatory store-house for the unreduced food; or the stomach itself has a protuberance in some part, or is strong and fleshy, so as to be able to store up the food for a considerable period and to concoct it, in spite of its not [30] having been ground into a pulp. For nature retrieves the inefficiency of the mouth by increasing the efficiency and heat of the stomach. Other birds there are, such, namely, as have long legs and live in marshes, that have none of these provisions, but merely an elongated oesophagus.15 The explanation of this is to be found in the moist character of their food. For all these birds feed on substances easy of reduction, and because of this, [their food being moist and not requiring much concoction]16 their stomachs are moist.

[675a1] Fishes are provided with teeth, which in almost all of them are of the saw-toothed kind. For there is but one small group in which it is otherwise. Of these the fish called Scarus is an example. And this is probably the reason why this fish [5] apparently ruminates, though no other fishes do so. For those horned animals that are not ambidentate also ruminate.

In fishes the teeth are all sharp; so that these animals can divide their food, though imperfectly. For it is impossible for a fish to linger or spend time in the act of mastication, and therefore they have no teeth that are flat or suitable for grinding; for such teeth would be to no purpose. The oesophagus again in some fishes is [10] entirely wanting, and in the rest is short. In order, however to facilitate the concoction of the food, some of them, as the mullet, have a fleshy stomach resembling that of a bird; while most of them have numerous appendages close against the stomach, to serve as a sort of antechamber in which the food may be stored up and undergo putrefaction and concoction. There is a contrast between [15] fishes and birds in the position of these appendages. For in fishes they are placed high up, close to the stomach; while in birds, if present at all, they are lower down, near the end of the gut. Some of the Vivipara also have appendages connected with the lower part of the gut which serve the same purpose as that stated above.

The whole tribe of fishes is of gluttonous appetite, owing to the arrangements [20] for the reduction of their food being very imperfect, and much of it consequently passing through them without undergoing concoction; and, of all, those are the most gluttonous that have a straight intestine. For as the passage of food in such cases is rapid, and the enjoyment derived from it in consequence but brief, it follows of necessity that the return of appetite is also speedy.

[25] It has already been mentioned that in ambidentates the stomach is of small size. It may be classed pretty nearly always under one or other of two headings, namely as resembling the stomach of the dog, or as resembling the stomach of the pig. In the pig the stomach is larger than in the dog, and presents certain folds of moderate size, the purpose of which is to lengthen out the period of concoction; while the stomach of the dog is of small size, not much larger in calibre than the gut, [30] and smooth on the internal surface.

For in all animals after the stomach comes the gut. This, like the stomach, presents numerous modifications. For in some animals it is uniform, when uncoiled, and alike throughout, while in others it differs in different portions. Thus in some cases it is wider in the neighbourhood of the stomach, and narrower towards the [35] other end; and this explains by the way why dogs have to strain so much in discharging their excrement. But in most animals it is the upper portion that is the [675b1] narrower and the lower that is of greater width.

Of greater length than in other animals, and much convoluted, are the intestines of those that have horns. These intestines, moreover, as also the stomach, are of ampler volume, in accordance with the larger size of the body. For animals with horns are, as a rule, large, because of the thorough elaboration which their food [5] undergoes. The gut, except in those animals where it is straight, invariably widens out as it gets farther from the stomach; then they have what is called the colon, and the blind and swollen part of the gut. After this it again becomes narrower and convoluted. Then succeeds a straight portion which runs right on to the vent. This [10] vent is known as the anus, and is in some animals surrounded by fat, in others not so. All these parts have been so contrived by nature as to harmonize with the various operations that relate to the food and its residue. For, as the residual food gets farther on and lower down, the space to contain it enlarges, allowing it to remain stationary and undergo conversion. Thus is it in those animals which, owing either [15] to their large size, or to the heat of the parts concerned, require more nutriment, and consume more fodder than the rest.

After this, just as a narrower gut succeeds to the upper stomach, so also does the residual food, when its juice is thoroughly exhausted, pass from the colon and the ample space of the lower stomach into a narrower channel and into the spiral [20] coil, in order that nature can regulate her expenditure and prevent the excremental residue from being discharged all at once.

In all such animals, however, as have to be comparatively moderate in their alimentation, the lower stomach presents no wide and roomy spaces, though their gut is not straight, but has a number of convolutions. For amplitude of space causes [25] desire for ample food, and straightness of the intestine causes quick return of appetite. And thus it is that all animals whose food receptacles are either simple or spacious are of gluttonous habits, the latter eating enormously at a meal, the former making meals at short intervals.

Again, since the food in the upper stomach, having just been swallowed, must of necessity be quite fresh, while that which has reached the lower stomach must [30] have had its juices exhausted and resemble dung, it follows of necessity that there must also be some intermediate part, in which the change may be effected, and where the food will be neither perfectly fresh nor yet dung. And thus it is that, in all [35] such animals as we are now considering, there is found what is called the jejunum; which is a part of the small gut which comes next to the stomach. For this jejunum lies between the upper cavity which contains the yet unconcocted food and the lower cavity which holds the useless residual matter. There is a jejunum in all these [676a1] animals, but it is plainly discernible in those of large size when they have abstained from food for a certain time. For then there is a sort of no-man’s land between the two regions, but when they have eaten the time occupied in the transition of food is but brief. In females this jejunum may occupy any part whatsoever of the upper [5] intestine, but in males it comes just before the caecum and the lower stomach.

15 · What is known as rennet is found in all animals that have a multiple stomach, and in the hare among animals whose stomach is single. In the former the rennet neither occupies the large paunch, nor the honeycomb bag, nor the terminal [10] reed, but is found in the cavity which separates this terminal one from the first, namely in the so-called manyplies. It is the thick character of their milk which causes all these animals to have rennet; whereas in animals with a single stomach the milk is thin, and consequently no rennet is formed. That is why the milk of [15] horned animals coagulates, while that of animals without horns does not. Rennet forms in the hare because it feeds on herbage that has juice like that of the fig; for juice of this kind coagulates the milk in the stomach of the sucklings. Why it is in the manyplies that rennet is formed in animals with multiple stomachs has been stated in the Problems.

BOOK IV

1 · The account which has now been given of the viscera, the stomach, and the other several parts holds equally good not only for the oviparous quadrupeds, [25] but also for such footless animals as the Serpents. These two classes of animals are indeed nearly akin, a serpent resembling a lizard which has been lengthened out and deprived of its feet. Fishes, again, resemble these two groups in all their parts, excepting that, while these, being land animals, have a lung, fishes have no lung, but [30] gills in its place. None of these animals, excepting the tortoise, as also no fish, has a bladder. For owing to the bloodlessness of their lung, they drink but sparingly; and such fluid as they have is diverted to the scaly plates, as in birds it is diverted to the feathers, and thus they come to have the same white matter on the surface of their excrement as we see on that of birds. For in animals that have a bladder, its [35] excretion when voided leaves a deposit of earthy brine in the containing vessel. For the sweet and fresh elements, being light, are expended on the flesh.

[676b1] Among the Serpents, the same peculiarity attaches to vipers, as among fishes attaches to Selachia. For both these and vipers are externally viviparous, but previously produce ova internally.

The stomach in all these animals is single, just as it is single in all other ambidentates; and their viscera are excessively small, as always happens when there [5] is no bladder. In serpents these viscera are, moreover, differently shaped from those of other animals. For, a serpent’s body being long and narrow, its contents are as it were moulded into a similar form, and thus come to be themselves elongated. [10]

All animals that have blood possess an omentum, a mesentery, intestines, and, moreover, a diaphragm and a heart; and all, excepting fishes, a lung and a windpipe. The relative positions, moreover, of the windpipe and the oesophagus are precisely similar in them all; and the reason is the same as has already been given. [15]

2 · Almost all sanguineous animals have a gall-bladder. In some this is attached to the liver, in others separated from that organ and attached to the intestines, being apparently in the latter case no less than in the former an appendage of the lower stomach. It is in fishes that this is most clearly seen. For all fishes have a gall-bladder; and in most of them it is attached to the intestine, being [20] in some, as in the bonito, united with this, like a border, along its whole length. It is similarly placed in most serpents. There are therefore no good grounds for the view entertained by some writers, that the gall exists for the sake of some sensory action. For they say that its use is to affect that part of the soul which is lodged in the neighbourhood of the liver, vexing this part so as to congeal it, and restoring it to [25] cheerfulness when it again flows free. But in some animals there is absolutely no gallbladder at all—in the horse, for instance, the mule, the ass, the deer, and the roe; and in others, as the camel, there is no distinct bladder, but merely small vessels of a biliary character. Again, there is no such organ in the seal, nor, among sea-animals, in the dolphin. Even within the limits of the same genus, some animals [30] appear to have and others to be without it. Such, for instance, is the case with mice; such also with man. For in some individuals there is a distinct gall-bladder attached to the liver, while in others there is no gall-bladder at all. This explains why there is a dispute about the group as a whole. For each observer, according as he has found it present or absent in the individual cases he has examined, has supposed it to be [35] present or absent in the whole genus. The same has occurred in the case of sheep and of goats. For these animals usually have a gall-bladder; but, while in some [677a1] localities it is so enormously big as to appear a monstrosity, as is the case in Naxos, in others it is altogether wanting, as is the case in a certain district belonging to the inhabitants of Chalcis in Euboea. Moreover, the gall-bladder in fishes is separated, [5] as already mentioned, by a considerable interval from the liver. No less mistaken seems to be the opinion of Anaxagoras and his followers, that the gall-bladder is the cause of acute diseases, inasmuch as it becomes over-full, and spurts out its excess on to the lung, the blood-vessels, and the ribs. For, almost invariably, those who suffer from these forms of disease are persons who have no gall-bladder at all, as would be quite evident were they to be dissected. Moreover, there is no kind of [10] correspondence between the amount of bile which is present in these diseases and the amount which is exuded. The most probable opinion is that, as the bile when it is present in any other part of the body is a mere residuum or a collipuescence, so also when it is present in the region of the liver it is a residue and not for the sake of [15] anything; just as is the case with the excretions of the stomach and intestines. For though even the residua are occasionally used by nature for some useful purpose, yet we must not in all cases expect to find such a final cause; for granted the existence of this or that constituent, with such and such properties, many results must ensue as necessary consequences of these properties. All animals, then, whose [20] liver is healthy in composition and supplied with none but sweet blood, are either entirely without a gall-bladder on this organ, or have merely small bile-containing vessels; or are some with and some without such parts. Thus it is that the liver in animals that have no gall-bladder is, as a rule, of good colour and sweet; and that, [25] when there is a gall-bladder, that part of the liver is sweetest which lies immediately underneath it. But, when animals are formed of blood less pure in composition, the bile is the residue left by this. For the very meaning of excrement is that it is the opposite of nutriment, and of bitter that it is the opposite of sweet; and healthy [30] blood is sweet. So that it is evident that the bile is not for the sake of anything, but is a purifying excretion. It was therefore no bad saying of old writers that the absence of a gall-bladder gave long life. In so saying they had in mind deer and animals with solid hoofs. For such have no gall-bladder and live long. But besides these there are other animals that have no gall-bladder, though those old writers had not noticed [35] the fact, such as the camel and the dolphin; and these also are in fact long-lived. Seeing, indeed, that the liver is a necessary and vital part in all animals that have [677b1] blood, it is but reasonable that on its character should depend the length or the shortness of life. Nor less reasonable is it that this organ and none other should have [5] such an excretion as the bile. For the heart, unable as it is to stand any violent affection, would be utterly intolerant of the proximity of such a fluid; and, as to the rest of the viscera, none excepting the liver are necessary parts of an animal. It would be absurd to think that phlegm and the sediment from the stomach are not residues wherever they are found; and clearly the same applies to bile too, and its [10] locality makes no difference.

3 · So much then of the gall-bladder, and of the reasons why some animals have one, while others have not. We have still to speak of the mesentery and the omentum; for these are associated with the parts already described and contained in [15] the same cavity. The omentum, then, is a membrane containing fat; the fat being suet or lard, according as the fat of the animal generally is of the former or latter description. What kinds of animals are so distinguished has been already set forth in an earlier part of this treatise. This membrane, alike in animals that have a single and in those that have a multiple stomach, grows from the middle of that organ, along a line which is marked on it like a seam. And it covers the rest of the stomach [20] and the greater part of the bowels, and this alike in all sanguineous animals whether they live on land or in water. Now the development of this part into such a form as has been described is the result of necessity. For, whenever dry and moist are mixed together and heated, the surface invariably becomes membranous and skin-like. But the region in which the omentum lies is full of nutriment of such a mixed character. Moreover, in consequence of the close texture of the membrane, that [25] portion of the sanguineous nutriment will alone filter into it which is of a greasy character; for this portion is composed of the finest particles; and it will be concocted by the heat of the part, and will be converted into suet or lard, and will not acquire a flesh-like or sanguineous constitution. The development, then, of the omentum occurs in this way. But it is used by nature to facilitate and to hasten the [30] concoction of food. For all that is hot aids concoction; and fat is hot, and the omentum is fat. This too explains why it hangs from the middle of the stomach; for the upper part of the stomach is assisted in concoction by the adjacent liver. Thus [35] much as concerns the omentum.

4 · The so-called mesentery is a membrane; and extends continuously from the long stretch of intestine to the great vessel and the aorta. In it are numerous and [678a1] close-packed vessels, which run from the intestines to the great vessel and to the aorta. The formation of this membrane we shall find to be the result of necessity, as is that of the other parts. What, however, is the cause of its existence in sanguineous [5] animals is manifest on reflection. For it is necessary that animals shall get nutriment from without; and, again, that this shall be converted into the ultimate nutriment, which is then distributed to the various parts; this ultimate nutriment being, in sanguineous animals, what we call blood, and having, in bloodless animals, no definite name. This being so, there must be channels through which the [10] nutriment shall pass, as it were through roots, from the stomach into the blood-vessels. Now the roots of plants are in the ground; for thence their nutriment is derived. But in animals the stomach and intestines represent the ground from which the nutriment is to be taken. The mesentery, then, is an organ to contain the [15] roots; and these roots are the vessels that traverse it. This then is the final cause of its existence. But how it absorbs nutriment, and how that portion of the food which enters into the vessels is distributed by them to the various parts of the body, are questions which will be considered when we come to deal with the generation and nutrition of animals. [20]

The constitution of sanguineous animals, so far as the parts as yet mentioned are concerned, and the reasons for such constitution, have now been set forth. In natural sequence we should next go on to the organs of generation, as yet undescribed, on which depend the distinctions of male and female. But, inasmuch as we shall have to deal specially with generation hereafter, it will be more convenient [25] to defer the consideration of these parts to that occasion.

5 · Very different from the animals we have as yet considered are the Cephalopoda and the Crustacea. For these have absolutely no viscera whatsoever; as is indeed the case with all bloodless animals, in which are included two other [30] genera, namely the Testacea and the Insects. For in none of them does the material out of which viscera are formed exist. None of them, that is, have blood. The cause of this lies in their substance. For the presence of blood in some animals, its absence from others, must be included in the formula which determines their respective [35] substances. Moreover, in the animals we are now considering, none of those final causes will be found to exist which in sanguineous animals determine the presence [678b1] of viscera. For they have no blood-vessels nor bladder, nor do they breathe; the only part that it is necessary for them to have being that which is analogous to a heart. For in all animals there must be some central and commanding part of the body, to lodge the sensory portion of the soul and the source of life. The organs of nutrition [5] are also of necessity present in them all. They differ, however, in character because of differences of the habitats in which they get their subsistence.

In the Cephalopoda there are two teeth, enclosing what is called the mouth; and inside this mouth is a flesh-like substance which represents a tongue and serves for the discrimination of pleasant and unpleasant food. The Crustacea have front [10] teeth in the same way, and also have the fleshy representative of a tongue. This latter part is found, moreover, in all Testacea for the same reason as in sanguineous animals, viz. to perceive their food. Similarly provided also are the Insects. For [15] some of these, such as the bees and the flies, have, as already described, their proboscis protruding from the mouth; while those others that have no such instrument in front have a similar part inside the mouth. Such, for instance, is the case in the ants and the like. As for teeth, some insects have them, the bees and the flies for instance, though in a somewhat modified form, while others that live on [20] fluid nutriment are without them. For in many insects the teeth are not meant to deal with the food, but to serve as weapons.

In some Testacea, as was said in the first treatise, the organ which is called the tongue is of considerable strength; and in sea-snails there are also two teeth, just as [25] in the Crustacea. The mouth in the Cephalopoda is succeeded by a long gullet. This leads to a crop, like that of a bird, and directly continuous with this is the stomach, from which a gut runs without windings to the vent. The cuttlefish and the octopus resemble each other completely, so far as regards the shape and consistency of these [30] parts. In the calamaries, as in the other groups, there are the two stomach-like receptacles; but the first of these cavities has less resemblance to a crop, and in neither is the form the same as in the other kinds, the whole body indeed being made of a softer kind of flesh.

The object of this arrangement of the parts in question is the same as in Birds; [35] for these also are all unable to masticate their food; and therefore it is that a crop precedes their stomach.

For purposes of defence, and to enable them to escape from their foes, the [679a1] Cephalopoda have what is called their ink. This is contained in a membranous pouch, which is attached to the body and provided with a terminal outlet just at the point where what is termed the funnel gives issue to the residua of the stomach. This [5] funnel is placed on the under surface of the animal. All Cephalopoda alike have this characteristic ink, but chief of all the cuttlefish, where it is more abundant than in the rest. When the animal is disturbed and frightened it uses this ink to make the surrounding water black and turbid, and so, as it were, puts a shield in front of its body.

In the Calamaries and the octopus the ink-bag is placed in the upper part of the body, in close proximity to the mytis, whereas in the cuttlefish it is lower down, against the stomach. For the cuttlefish has a more plentiful supply of ink than the [10] rest, inasmuch as it makes more use of it. The reasons for this are that it lives near the shore, and that it has no other means of protection; whereas the octopus has its tentacles to use in its defence, and is, moreover, endowed with the power of changing colour. This changing of colour, like the discharge of ink, occurs as the result of fright. As to the calamary, it lives far out at sea, being the only one of the [15] Cephalopoda that does so. Thus the ink is more abundant in the cuttlefish, and this greater abundance explains the lower position; for it allows the ink to be ejected with ease even from a distance. The ink itself is of an earthy character, in this resembling the white deposit on the surface of a bird’s excrement, and the explanation in both cases is the same, namely, the absence of a bladder. For it is the ink that serves for the excretion of the earthiest matter. And this is more especially [20] the case in the cuttlefish, because there is a greater proportion of earth in its composition. The earthy character of its bone is a clear indication of this. For in the octopus there is no bone at all, and in the calamary it is thin and cartilaginous. (Why this bone should be present in some Cephalopoda, and wanting in others, and how its character varies in those that have it, has been explained.)

These animals, having no blood, are in consequence cold and of a timid [25] character. Now, in some animals, fear causes a disturbance of the bowels, and, in others, a flow of urine from the bladder. Similarly in these it produces a discharge of ink, and, though the ejection is the result of necessity, like the discharge of urine, yet at the same time nature makes use of this residue for the protection and safety of the [30] animal.

The Crustacea also, both the crayfish and the crabs, are provided with two anterior teeth and between these the tongue-like piece of flesh, as has indeed been already mentioned. Directly after their mouth comes a gullet, which is small in proportion to the body; and then a stomach, which in the crayfish and some of the [35] crabs is furnished with a second set of teeth, the anterior teeth being insufficient for adequate mastication. From the stomach a uniform gut runs in a direct line to the [679b1] excremental vent.

The parts described are to be found also in all the various Testacea. The degree of distinctness, however, with which they are formed varies in the different kinds, and the larger the size of the animal the more easily distinguishable are all these parts severally. In the sea-snails, for example, we find teeth, hard and sharp, as [5] before mentioned, and between them the flesh-like substance, just as in the Crustacea and Cephalopoda, and again the proboscis, which, as has been stated, is something between a sting and a tongue. Directly after the mouth comes a kind of bird-like crop, then a gullet, succeeded by a stomach, in which is the ‘poppy’, as it is [10] styled; and continuous with this is an intestine, starting directly from it. It is this residual substance which appears in all the Testacea to form the most palatable morsel. The purple murex, the trumpet-shell, and the other spiral-shells resemble [15] the sea-snail. The genera and species of Testacea are very numerous. For there are those with spiral shells, of which some have just been mentioned; and, besides these, there are bivalves and univalves. Those with spiral shells may, indeed, after a certain fashion be said to resemble bivalves. For they all from their very birth have an operculum over that part of their body which is exposed to view. This is the case [20] with the purple murex, the trumpet-shell, the nerites, and the like. Were it not for this, the part which is undefended by the shell would be very liable to injury by collision with external objects. The univalves also are not without protection. For on their upper surface they have a shell, and they attach themselves to the rocks, and so [25] after a manner become bivalved by virtue of this borrowed protection. Of these the animals known as limpets are an example. The bivalves, scallops and mussels, for instance, are protected by the power they have of closing their valves; and the spiral-shells by the operculum just mentioned, which transforms them, as it were, from univalves into bivalves. But of all there is none so perfectly protected as the sea-urchin. For here there is a shell which encloses the body completely, and which [30] is, moreover, set with sharp spines. This peculiarity distinguishes the sea-urchin from all other Testacea, as has already been mentioned.

The structure of the Testacea and of the Crustacea is exactly the reverse of that of the Cephalopoda. For in the latter the fleshy substance is on the outside and the earthy substance within, whereas in the former the soft parts are inside and the hard part without. In the sea-urchin, however, there is no fleshy part whatsoever.

[35] All the other Testacea also possess, as has been said, a mouth with the tongue-like body, a stomach, and a vent for excrement, but they differ from each [680a1] other in the positions and proportions of these parts. The details, however, of these differences must be looked for in the History of Animals and the Anatomies. For while there are some points which can be made clear by verbal description, there are others which are more suited for ocular demonstration.

[5] Peculiar among the Testacea are the sea-urchins and the animals known as ascidians. The sea-urchins have five teeth, and in the centre of these the fleshy body which is common to all the animals we have been discussing. Immediately after this comes a gullet, and then the stomach, divided into a number of separate compartments, which look like so many distinct stomachs; for the cavities are separate and [10] all contain abundant residual matter. They are all, however, connected with one and the same oesophagus, and they all end in one and the same excremental vent. There is nothing besides the stomach of a fleshy character, as has already been stated. All that can be seen are the so-called eggs, of which there are several, contained each in a separate membrane, and certain black bodies which have no name, and which, beginning at the animal’s mouth, are scattered round its body here and there. These [15] sea-urchins are not all of one species, but there are several different kinds, and in all of them the parts mentioned are to be found. It is not, however, in every kind that the so-called eggs are edible. Neither do these attain to any size in any other species than that with which we are all familiar. A similar distinction may be made [20] generally in the case of all Testacea. For there is a great difference in the edible qualities of the flesh of different kinds; and in some, moreover, the residual substance known as the poppy is good for food, while in others it is uneatable. This in the spiral kinds is lodged in the spiral part of the shell, while in univalves, such as limpets, it occupies the fundus, and in bivalves is placed near the hinge, the so-called egg lying on the right; while on the opposite side is the vent. The former is [25] incorrectly termed egg, for it merely corresponds to what in well-fed sanguineous animals is fat; and thus it is that it makes its appearance at those seasons of the year when they are in good condition, namely, spring and autumn. For no Testacea can abide extremes of temperature, and they are in evil plight in seasons of great cold or [30] heat. This is clearly shown by what occurs in the case of the sea-urchins. For though the eggs are to be found in these animals even directly they are born, yet they acquire a greater size than usual at the time of full moon; not, as some think, because sea-urchins eat more at that season, but because the nights are then warmer, owing to the moonlight. For these creatures are bloodless, and so are unable to stand cold and require warmth. That is why they are found in better condition in summer everywhere except in the Pyrrhean tidal strait. There the [680b1] sea-urchins flourish as well in winter as in summer. But the reason for this is that they have a greater abundance of food in the winter, because the fish desert the strait at that season.

The number of the eggs is the same in all sea-urchins, and is an odd one. For there are five ova, just as there are also five teeth and five stomachs; and the [5] explanation of this is to be found in the fact that the eggs are not really eggs, but merely, as was said before, the result of the animal’s well-fed condition. Oysters also have a so-called egg, corresponding in character to that of the sea-urchins, but existing only on one side of their body. Now inasmuch as the sea-urchin is of a spherical form, and not merely a single disk like the oyster, and in virtue of its [10] spherical shape is the same from whatever side it be examined, its egg must necessarily be of a corresponding symmetry. For the spherical shape has not the asymmetry of the disk-shaped body of the oysters. For in all these animals the head is central, but in the sea-urchin it is at the top. But even so the egg cannot be [15] continuous—for it is not so in the others—but is on one side of the disk only. Thus since this is a common property of them all and the sea-urchin is peculiar in being spherical, this animal cannot possibly have an even number of eggs. For were they an even number, they would have to be arranged exactly opposite to each other, so as to keep the necessary symmetry; and in that case there would be eggs on both [20] sides of the disk. But this is not the case in any of the other shell-fish. For both in the oysters and in the scallops we find the egg only on one side of the circumference. The number then must be uneven, three for instance, or five. But if there were only three they would be much too far apart; while, if there were more than five, they [25] would come to form a continuous mass. The former arrangement would not be for the animal’s good, the latter would not be possible. There can therefore be neither more nor less than five. For the same reason the stomach is divided into five parts, and there is a corresponding number of teeth. For seeing that the eggs represent each of them a kind of body for the animal, their disposition must conform to that of [30] the stomach, seeing that it is from this that they derive the material for their growth. Now if there were only one stomach, either the eggs would be too far off from it, or it would be so big as to fill up the whole cavity, and the sea-urchin would have great difficulty in moving about and finding due nourishment for its repletion. As then there are five intervals so are there of necessity five divisions of the stomach, one for each interval. So also, and on like grounds, there are five teeth. For [681a1] nature is thus enabled to allot one alike to each of the aforementioned parts. These, then, are the reasons why the number of eggs in the sea-urchin is an odd one, and why that odd number is five. In some sea-urchins the eggs are excessively small, in others of considerable size, the explanation being that the latter are of a warmer [5] constitution, and so are able to concoct their food more thoroughly; and that is why the inedible ones tend to be full of residue. Those of a warmer constitution are, moreover, in virtue of their warmth more given to motion, so that they make expeditions in search of food, instead of remaining stationary like the rest. As evidence of this, it will be found that they always have something or other sticking to their spines, as though they moved much about; for they use their spines as feet.

[10] The ascidians differ but slightly from plants, and yet have more of an animal nature than the sponges, which are plants and nothing more. For nature passes from lifeless objects to animals in such unbroken sequence, interposing between them beings which live and yet are not animals, that scarcely any difference seems to [15] exist between two neighbouring groups owing to their close proximity.

A sponge, then, as already said, in these respects completely resembles a plant, that throughout its life it is attached to a rock, and that when separated from this it dies. Slightly different from the sponges are the so-called Holothurias and the sea-lungs, as also sundry other sea-animals that resemble them. For these are free [20] and unattached. Yet they have no sensation, and their life is simply that of a plant separated from the ground. For even among landplants there are some that spring up and grow, either upon other plants, or even entirely free. Such, for example, is the plant which is found on Parnassus, and which some call the rockplant. This you may hang up on a peg and it will yet live for a considerable time. Sometimes [25] ascidians and the like so far resemble plants as that they never live free and unattached, but, on the other hand, inasmuch as they have a certain flesh-like substance, they must be supposed to possess some degree of sensibility—and it is unclear whether they are to be classed as plants or as animals.

An ascidian has a body divided by a single septum and with two orifices, one [30] where it takes in the fluid matter that ministers to its nutrition, the other where it discharges the surplus juice, for it has no visible residual substance, such as have the other Testacea. This is itself a very strong justification for considering an ascidian, and anything else there may be among animals that resembles it, to be a plant; for plants also never have any residuum. Across the middle of the body of these there [35] runs a thin transverse partition, and here it is that we may reasonably suppose the part on which life depends to be situated.

The sea-anemones or sea-nettles, as they are variously called, are not Testacea [681b1] at all, but lie outside the recognized groups. Their constitution approximates them on one side to plants, on the other to animals. For seeing that some of them can [5] detach themselves and can fasten upon their food, and that they are sensible of objects which come in contact with them, they must be considered to have an animal nature. The like conclusion follows from their using the asperity of their bodies as a protection against their enemies. But, on the other hand, they are closely allied to plants, firstly by the imperfection of their structure, secondly by their being able to attach themselves to the rocks, which they do with great rapidity, and lastly by their having no visible residuum notwithstanding that they possess a mouth.

Very similar again are the Starfishes. For these also fasten on their prey, and suck out its juices, and thus destroy a vast number of oysters. At the same time they [10] present a certain resemblance to such of the animals we have described as the Cephalopoda and Crustacea, inasmuch as they are free and unattached. The same may also be said of the Testacea.

Such, then, is the structure of the parts that minister to nutrition and which every animal must necessarily possess. But besides these organs it is quite plain that in every animal there must be some part or other which shall be analogous to what [15] in sanguineous animals is the presiding seat of sensation. In the Cephalopoda this part consists of a fluid substance contained in a membrane, through which runs the gullet on its way to the stomach. It is attached to the body rather towards its upper surface, and by some is called the mytis. Just such another organ is found also in the [20] Crustacea and there too is known by the same name. This part is at once fluid and corporeal and, as before said, is traversed by the gullet. For had the gullet been placed between the mytis and the upper surface of the animal, the hardness of the back would have interfered with its due dilatation as the food enters. On the outer [25] surface of the mytis runs the intestine; and in contact with this latter is placed the ink-bag, so that it may be removed as far as possible from the mouth and its obnoxious fluid be kept at a distance from the nobler and sovereign part. The position of the mytis shows that it corresponds to the heart of sanguineous animals; for it occupies the self-same place. The same is shown by the sweetness of its fluid, [30] which has the character of concocted matter and resembles blood.

In the Testacea the presiding seat of sensation is in a corresponding position, but is less easily made out. It should, however, always be looked for in some midway position; namely, in such Testacea as are stationary, midway between the part by which food is taken in and the channel through which either the excrement or the spermatic fluid is voided, and, in those species which are capable of locomotion, [682a1] invariably midway between the right and left sides.

In Insects the organ which is the seat of sensation, lies, as was stated in the first treatise, between the head and the cavity which contains the stomach. In most of them it consists of a single part; but in others, for instance in such as have long bodies and resemble the centipede, it is made up of several parts, so that such insects [5] continue to live after they have been cut in pieces. For the aim of nature is to give to each animal only one such dominant part; and when she can, she makes it a unity; when she cannot, a plurality. This is much more clearly marked in some insects than in others.

The parts concerned in nutrition are not alike in all insects, but show considerable diversity. Thus some have what is called a sting in the mouth, which is [10] a kind of compound instrument that combines in itself the character of a tongue and of lips. In others that have no such instrument in front there is a part behind the teeth that answers the same sensory purposes. Immediately after the mouth comes the intestine, which is never wanting in any insect. This runs in a straight line and [15] without further complication to the vent; occasionally, however, it has a spiral coil. There are, moreover, some insects in which a stomach succeeds to the mouth, and is itself succeeded by a convoluted intestine, so that the larger and more voracious insects may be enabled to take in a more abundant supply of food. More peculiar [20] than any are the Cicadae. For here the mouth and the tongue are united so as to form a single part, through which, as through a root, the insect sucks up the fluids on which it lives. Insects are always small eaters, not so much because of their diminutive size as because of their cold temperament. For it is heat which requires sustenance; just as it is heat which speedily concocts it. But cold requires no [25] sustenance. In no insects is this so conspicuous as in these Cicadae. For they find enough to live on in the moisture which is deposited from the air. So also do the Ephemera that are found about the Black Sea. But while these latter only live for a single day, the Cicadae subsist on such food for several days, though still not many.

[30] We have now done with the internal parts of animals, and must therefore return to the consideration of the external parts which have not yet been described. It will be better to begin with the animals we have just been describing, rather than from the point at which we left off, so that proceeding from these, which require less discussion, our account may have more time to spend on the perfect kinds of animals, those namely that have blood.

[35] 6 · Insects, though they present no great multiplicity of parts, are not without diversities when compared with each other. They are all many-footed; the [682b1] object of this being to compensate their natural slowness and frigidity, and give greater activity to their motions. Accordingly we find that those which, as the centipedes, have long bodies, and are therefore the most liable to refrigeration, have also the greatest number of feet. Again, the body in these animals is insected—the [5] reason for this being that they have not got one vital centre but many—and the number of their feet corresponds to that of the insections.17

Should the feet fall short of this, their deficiency is compensated by the power of flight. Of such flying insects some live a wandering life, and are forced to make long expeditions in search of food. These have a body of light weight, and four [10] wings, two on either side, to support it. Such are bees and the insects akin to them; for they have two wings on each side. When, however, such insects are of very small bulk, their wings are reduced to two, as is the case with flies. Insects with heavy bodies and of stationary habits, though not polypterous in the same way as bees, yet have sheaths to their wings to maintain their efficiency. Such are the Melolonthae [15] and the like. For their stationary habits expose their wings to much greater risks than are run by those of insects that are more constantly in flight, and on this account they are provided with this protecting shield. The wing of an insect has neither divisions nor shaft. For it is no wing at all, but merely a skin-like membrane that, owing to its dryness, necessarily becomes detached from the surface of the [20] body, as the fleshy substance grows cold.

These animals then have their bodies insected, not only for the reasons already assigned, but also to enable them to curl round in such a manner as may protect them from injury; for such insects as have long bodies can roll themselves up, which would be impossible were it not for the insections; and those that cannot do this can yet draw their segments up and so increase the hardness of their bodies. This can be felt quite plainly by putting the finger on one of the insects, for instance, known as [25] dung-beetles. The touch frightens the insect, and it remains motionless, while its body becomes hard. The division of the body into segments is necessary; for that they have several controlling sources is a constituent of their substances, and is a character which approximates them to plants. For as plants, though cut into pieces, [30] can still live, so also can insects. There is, however, this difference between the two cases, that the portions of the divided insect live only for a limited time, whereas the portions of the plant actually attain the perfect form of the whole, so that from one single plant you may obtain two or more.

Some insects are also provided with another means of protection against their enemies, namely a sting. In some this is in front, connected with the tongue, in [35] others behind at the posterior end. For just as the organ of smell in elephants answers several uses, serving alike as a weapon and for purposes of nutrition, so does [683a1] also the sting, when placed in connexion with the tongue, as in some insects, answer more than one end. For it is the instrument through which they derive their sensations of food, as well as that with which they suck it up and bring it to the mouth. Such of these insects as have no anterior sting are provided with teeth, which serve in some of them for biting the food, and in others for its prehension and [5] conveyance to the mouth. Such are their uses, for instance, in ants and all the various kinds of bees. As for the insects that have a sting behind, this weapon is given them because they are of a fierce disposition. In some of them the sting is lodged inside the body, in bees, for example, and wasps. For these insects are made for flight, and were their sting external and of delicate make it would soon get [10] spoiled; and if, on the other hand, it were of thicker build, as in scorpions, its weight would be an incumbrance. As for scorpions that live on the ground and have a tail, their sting must be set upon this, as otherwise it would be of no use as a weapon. Dipterous insects never have a posterior sting. For the very reason of their being [15] dipterous is that they are small and weak, and therefore require no more than two feathers to support their light weight; and for the same reason their sting is in front; for their strength is not sufficient to allow them to strike efficiently with the hinder part of their body. Polypterous insects, on the other hand, are of greater bulk and hence have more wings and are stronger in their hinder parts. Now it is better, when possible, that one and the same instrument shall not be made to serve several [20] dissimilar uses; but that there shall be one organ to serve as a weapon, which can then be very sharp, and a distinct one to serve as a tongue, which can then be of spongy texture and fit to absorb nutriment. Whenever, therefore, nature is able to provide two separate instruments for two separate uses, without the one hampering the other, she does so, instead of acting like a coppersmith who for cheapness makes [25] a spit and lampholder in one. It is only when this is impossible that she uses one organ for several functions. The anterior legs are in some cases longer than the others, that they may serve to wipe away any foreign matter that may lodge on the insect’s eyes; for their sight is not very distinct owing to the eyes being made of a [30] hard substance. Flies and bees and the like may be constantly seen thus dressing themselves with crossed forelegs. Of the other legs, the hinder are bigger than the middle pair, both to aid in walking and also that the insect, when it takes flight, may spring more easily from the ground. This difference is still more marked in such insects as leap, in locusts for instance, and in the various kinds of fleas. For these first bend and then extend the legs, and, by doing so, are necessarily shot up from [683b1] the ground. It is only the hind legs of locusts, and not the front ones, that resemble the steering oars of a ship. For this requires that the joint shall be deflected inwards, and such is never the case with the anterior limbs. The whole number of legs, including those used in leaping, is six in all these insects.

[5] 7 · In the Testacea the body consists of but few parts, the reason being that these animals live a stationary life. For such animals as move much about must of necessity have more numerous parts than such as remain quiet; for their activities are many, and the more the movements the greater the number of organs required to effect them. Some species of Testacea are absolutely motionless, and others not [10] quite but nearly so. Nature, however, has provided them with a protection in the hardness of the shell with which she has invested their body. This shell, as already has been said, may have one valve, or two valves, or be spiral. In the latter case it may be either helical, as in trumpet-shells, or spherical, as in sea-urchins. When it [15] has two valves, these may be gaping, as in scallops and mussels, where the valves are united together on one side only, so as to open and shut on the other; or they may be united together on both sides, as in the razor-fish. In all cases alike the Testacea [20] have, like plants, the head downwards. The reason for this is, that they take in their nourishment from below, just as do plants with their roots. Thus the under parts come in them to be above, and the upper parts to be below. The body is enclosed in a membrane, and through this the animal filters fresh water and absorbs its nutriment. In all there is a head; but none of the parts, excepting this recipient of food, has any distinctive name.

[25] 8 · All the Crustacea can crawl as well as swim, and accordingly they are provided with numerous feet. There are four main genera, viz. the crayfish, the lobsters, the prawns, and the crabs. In each of these genera, again, there are numerous species, which differ from each other not only as regards shape, but also [30] very considerably as regards size. For, while in some species the individuals are large, in others they are excessively minute. The crabs and crayfish resemble each other in possessing claws. These claws are not for locomotion, but to serve in place of hands for seizing and holding objects; and they are therefore bent in the opposite direction to the feet, being so twisted as to turn their convexity towards the body, [35] while their feet turn towards it their concavity. For in this position the claws are best suited for laying hold of the food and carrying it to the mouth. The distinction [684a1] between the crayfish and the crabs consists in the former having a tail while the latter have none. For the crayfish swim about and a tail is therefore of use to them, serving for their propulsion like the blade of an oar. But it would be of no use to the crabs; for these animals live habitually close to the shore, and creep into holes and [5] corners. In such of them as live out at sea, the feet are much less adapted for locomotion than in the rest, because they are little given to moving about but depend for protection on their shell-like covering. The Maiae and the crabs known [10] as Heracleotic are examples of this; the legs in the former being very thin, in the latter very short.

The very minute crabs that are found among the small fry have their hindermost feet flattened out into the semblance of fins or oar-blades, so as to help the animal in swimming.

The prawns are distinguished from the crabs by the presence of a tail; and from the crayfish by the absence of claws. This is explained by their large number of feet, [15] on which has been expended the material for the growth of claws. Their feet again are numerous to suit their mode of progression, which is mainly by swimming.

Of the parts on the under surface, those near the head are in some of these animals formed like gills, for the admission and discharge of water; while the parts [20] lower down in the female crayfish are more laminar than in the males, and in the female crabs the flap is furnished with hairier appendages. For the females retain their eggs in these parts instead of letting them go free, as do fishes and all other oviparous animals; for the appendages are broader and provide more room for the [25] eggs. In the crayfish and in the crabs the right claw is invariably the larger and the stronger. For it is natural to every animal in active operations to use the parts on its right side in preference to those on its left; and nature invariably assigns each organ, either exclusively or in a more perfect condition, to such animals as can use it. So it is with tusks, and teeth, and horns, and spurs, and all such defensive and offensive [30] weapons.

In the lobsters alone it is a matter of chance which claw is the larger, and this in either sex. Claws they must have, because they belong to a genus in which this is a constant character; but they have them in this indeterminate way, owing to imperfect formation and to their not using them for their natural purpose, but for [684b1] locomotion.

For a detailed account of the several parts of these animals, of their position and their differences, those parts being also included which distinguish the sexes, reference must be made to the Anatomies and to the History of Animals. [5]

9 · We come now to the Cephalopoda. Their internal organs have already been described with those of other animals. Externally there is the trunk of the body, not distinctly defined, and in front of this the head surrounded by feet, which [10] form a circle about the mouth and teeth, and are set between these and the eyes. Now in all other animals the feet, if there are any, are disposed in one of two ways; either before and behind or along the sides, the latter being the plan in such of them, for instance, as are bloodless and have numerous feet. But in the Cephalopoda there is a peculiar arrangement, different from either of these. For their feet are all placed at what may be called the fore end. The reason for this is that the hind part of [15] their body has been drawn up close to the fore part, as is also the case in the spiral Testacea. For the Testacea, while in some points they resemble the Crustacea, in others resemble the Cephalopoda. Their earthy matter is on the outside, and their fleshy substance within. So far they are like the Crustacea. But the general plan of [20] their body is that of the Cephalopoda; and, though this is true in a certain degree of all the Testacea, it is more especially true of those turbinated species that have a spiral shell. For18 both classes have this nature; and that is why they walk evenly, [25] unlike quadrupeds and men. Now men have their mouth in their head, i.e. in the upper part of their body; next comes the gullet, then the stomach, then the gut which extends to the vent for the residue. That is the arrangement in the sanguinea, i.e. the head is followed by what is called the thorax and the parts about it; the remaining parts, such as the anterior and posterior limbs, having been superadded [30] by nature, to minister to these and for locomotion.

In the Crustacea also and in Insects there is a tendency to a similar arrangement of the internal parts in a straight line; the distinction between these groups and the sanguineous animals depending on differences of the external organs which minister to locomotion. But the Cephalopoda and the spiral Testacea have in [685a1] common an arrangement which stands in contrast with this. For here the two extremities are brought together by a curve, as if one were to bend the straight line until D came close to A. Such, then, is the disposition of the internal parts; and [5] round these, in the Cephalopoda, is placed the sac (in the octopus alone called a head), and, in the Testacea, the spiral shell which corresponds to the sac. There is, in fact, only this difference between them, that the investing substance of the Cephalopoda is soft while the shell of the Testacea is hard, nature having surrounded their fleshy part with this hard coating as a protection because of their [10] limited power of locomotion. For this reason, in both classes the excrement is voided near the mouth; at a point below this orifice in the Cephalopoda, and in the spiral-shells on one side of it.

Such, then, is the explanation of the position of the feet in the Cephalopoda, and of the contrast they present to other animals in this matter. The arrangement, however, in the cuttlefish and the calamaries is not precisely the same as in the [15] octopus, owing to the former having no other mode of progression than by swimming, while the latter not only swim but crawl. For in the former six of the feet are above the teeth and small, the outer one on either side being the biggest; while the remaining two of the eight are below the mouth and are the biggest of all, just as the hind limbs in quadrupeds are stronger than the fore limbs. For it is these that [20] have to support the weight, and to take the main part in locomotion. And the outer two are bigger than the pair which intervene between them because they have to assist the lowermost pair in their office. In the octopus, on the other hand, the four central feet are the biggest. Again, though the number of feet is the same in all the Cephalopoda, namely eight, their length varies in different kinds, being short in the cuttlefish and the calamaries, but greater in the octopus. For in these latter the trunk of the body is of small bulk, while in the former it is of considerable size; and [25] so in the one case nature has used the materials subtracted from the body to give length to the feet, while in the other she has given to the growth of the body what she has first taken from the feet. The octopus then, owing to the length of their feet, can not only swim but crawl, whereas in the other genera the feet are useless for the latter mode of progression, being small while the bulk of the body is considerable. [30] These short feet would not enable their possessors to cling to the rocks and keep themselves from being torn off by the waves when these run high in times of storm; neither would they serve to lay hold of objects at all remote and bring them in; but, to supply these defects, the animal is furnished with two long proboscises, by which it can moor itself and ride at anchor like a ship in rough weather, and by which it can catch prey at a distance and to bring it to the mouth. They are so used by both [685b1] the cuttlefish and the calamaries. In the octopus the feet are themselves able to perform these offices, and there are consequently no proboscises. Some animals have suckers and tentacles as well as feet; and these have the same capacity and [5] structure as those plaited instruments which were used by physicians of old to reduce dislocations of the fingers. Like these they are made by the interlacing of their fibres, and they act by pulling upon pieces of flesh and yielding substances. For they encircle an object in a slackened condition, and when they are put on the stretch they grasp and cling tightly to whatever it may be that is in contact with their inner surface. Since, then, the Cephalopoda have no other instruments with [10] which to convey anything to themselves from without, than either feet, as in some species or proboscises as in others, they are provided with these to serve as hands for offence and defence and other uses.

The suckers are set in double line in all the Cephalopoda excepting in one kind of octopus where there is but a single row. The length and the slimness which is part of the nature of this kind of octopus explain the exception. For a narrow space cannot possibly admit of more than a single row. This exceptional character, then, belongs to them, not because it is the most advantageous arrangement, but because [15] it is the necessary consequence of the special nature of their substance.

In all these animals there is a fin, encircling the sac. In the octopus and the cuttlefish this fin is unbroken and continuous, as is also the case in the larger calamaries. But in the smaller kind, called Teuthides, the fin is not only broader than in the cuttlefish and the octopus where it is narrow, but, moreover, does not [20] encircle the entire sac, but only begins in the middle of the side. The use of this fin is to enable the animal to swim, and also to direct its course. It acts, that is, like the rump-feathers in birds, or the tail-fin in fishes. In none is it so small or so indistinct as in the octopus. For in these the body is of small bulk and can be steered by the [25] feet sufficiently well.

The Insects, the Crustacea, the Testacea, and the Cephalopoda, have now been dealt with in turn; and their parts have been described, whether internal or external.

[30] 10 · We must now go back to the vivipara that have blood, and consider such of their parts, already enumerated, as were before passed over. When we have done with these, we will pass on to the oviparous sanguinea, and treat of them in like manner.

[35] The parts that border on the head, and on what is known as the neck and throat, have already been taken into consideration. All animals that have blood [686a1] have a head; whereas in some bloodless animals, such as crabs, the part which represents a head is not clearly defined. As to the neck, it is present in all the Vivipara, but only in some of the Ovipara; for while those that have a lung also have [5] a neck those that do not inhale the outer air have none.

The head exists mainly for the sake of the brain. For every animal that has blood must of necessity have a brain; and must, moreover, for reasons already given, have it placed in an opposite region to the heart. But the head has also been chosen [10] by nature as the part in which to set some of the senses; because its blood is mixed in such suitable proportions as to ensure their tranquillity and precision, while at the same time it can supply the brain with such warmth as it requires. There is yet a third constituent superadded to the head, namely the part which ministers to the ingestion of food. This has been placed here by nature, because such a situation accords best with the general configuration of the body. For the stomach could not [15] possibly be placed above the heart, seeing that this is the sovereign organ; and if placed below, as in fact it is, then the mouth could not possibly be placed there also. For this would have necessitated a great increase in the length of the body; and the stomach, moreover, would have been removed too far from the source of motion and of concoction.

The head, then, exists for the sake of these three parts; while the neck, again, [20] exists for the sake of the windpipe. For it acts as a defence to this and to the oesophagus, encircling them and keeping them from injury. In all other animals this neck is flexible and contains several vertebrae; but in wolves and lions it contains only a single bone. For the object of nature was to give these animals an organ which should be serviceable in the way of strength, rather than for other purposes.

[25] Continuous with the head and neck is the trunk with the anterior limbs. In man the forelegs and forefeet are replaced by arms and by what we call hands. For of all animals man alone stands erect, in accordance with his god-like nature and substance. For it is the function of the god-like to think and to be wise; and no easy [30] task were this under the burden of a heavy body, pressing down from above and obstructing by its weight the motions of the intellect and of the general sense. When, moreover, the weight and corporeal substance become excessive, the body must of necessity incline towards the ground. In such cases therefore nature, in order to give support to the body, has replaced the arms and hands by forefeet, and has thus converted the animal into a quadruped. For, as every animal that walks [686b1] must of necessity have the two hinder feet, such an animal becomes a quadruped, its body inclining downwards in front from the weight which its soul cannot sustain. For all animals, man alone excepted, are dwarf-like in form. For the dwarf-like is that in which the upper part is large, while that which bears the weight and is used [5] in progression is small. This upper part is what we call the trunk, which reaches from the mouth to the vent. In man it is duly proportionate to the part below, and diminishes much in its comparative size as the man attains to full growth. But in his infancy the contrary obtains, and the upper parts are large, while the lower part is small, so that the infant can only crawl, and is unable to walk; and at first cannot [10] even crawl, but remains without motion. For all children are dwarfs in shape, but cease to be so as they become men, from the growth of their lower part; whereas in quadrupeds the reverse occurs, their lower parts being largest in youth, and advance of years bringing increased growth above, that is in the trunk, which extends from the rump to the head. Thus it is that foals are scarcely, if at all, below horses in [15] height; and that while still young they can touch their heads with the hind legs, though this is no longer possible when they are older. Such, then, is the form of animals that have either a solid or a cloven hoof. But such as are polydactylous and without horns, though they too are of dwarf-like shape, are so in a less degree; and therefore the greater growth of the lower parts as compared with the upper is also small, being proportionate to this smaller deficiency. [20]

Dwarf-like again is the race of birds and fishes; and so in fact, as already has been said, is every animal that has blood. This is the reason why no other animal is so intelligent as man. For even among men themselves if we compare children with adults, or such adults as are of dwarf-like shape with such as are not, we find that, whatever other superiority the former may possess, they are at any rate deficient as [25] compared with the latter in intelligence. The explanation, as already stated, is that in many their psychical principle is corporeal and impeded in its motions. Let now a further decrease occur in the elevating heat, and a further increase in the earthly matter, and the animals become smaller in bulk, and their feet more numerous, [30] until at a later stage they become footless and extended full length on the ground. Then, by further small successions of change, they come to have their principal organ below; and at last the part which answers to a head becomes motionless and destitute of sensation. Thus the animal becomes a plant, that has its upper parts downwards and its lower parts above. For in plants the roots are the equivalents of mouth and head, while the seed has an opposite significance, for it is produced [687a1] above at the extremities of the twigs.

The reasons have now been stated why some animals have many feet, some only two, and others none; why, also, some living things are plants and others animals; and, lastly, why man alone of all animals stands erect. Standing thus erect, [5] man has no need of legs in front, and in their stead has been endowed by nature with arms and hands. Now it is the opinion of Anaxagoras that the possession of these hands is the cause of man being of all animals the most intelligent. But it is more rational to suppose that man has hands because of his superior intelligence. For the [10] hands are instruments, and the invariable plan of nature in distributing the organs is to give each to such animal as can make use of it; nature acting in this matter as any prudent man would do. For it is a better plan to take a person who is already a flute-player and give him a flute, than to take one who possesses a flute and teach him the art of flute-playing. For nature adds that which is less to that which is [15] greater and more important, and not that which is more valuable and greater to that which is less. Seeing then that such is the better course, and seeing also that of what is possible nature invariably brings about the best, we must conclude that man does not owe his superior intelligence to his hands, but his hands to his superior intelligence. For the most intelligent of animals is the one who would put the most [20] organs to good use; and the hand is not to be looked on as one organ but as many; for it is, as it were, an instrument for further instruments. This instrument, therefore,—the hand—of all instruments the most variously serviceable, has been given by nature to man, the animal of all animals the most capable of acquiring the most varied arts.

Much in error, then, are they who say that the construction of man is not only [25] faulty, but inferior to that of all other animals; seeing that he is, as they point out, barefooted, naked, and without weapon of which to avail himself. For other animals have each but one mode of defence, and this they can never change; so that they must perform all the offices of life and even, so to speak, sleep with sandals on, never laying aside whatever serves as a protection to their bodies, nor changing such single weapon as they may chance to possess. But to man numerous modes of defence are [687b1] open, and these, moreover, he may change at will; as also he may adopt such weapon as he pleases, and at such places as suit him. For the hand is talon, hoof, and horn, at will. So too it is spear, and sword, and whatsoever other weapon or instrument you [5] please; for all these can it be from its power of grasping and holding them all. In harmony with this varied office is the form which nature has contrived for it. For it is split into several divisions, and whereas being compounded is contained in being divided, the reverse is not the case. The divisions also may be used singly or two [10] together and in various combinations. The joints, moreover, of the fingers are well constructed for prehension and for pressure. One of these also, short and thick but not long, is placed laterally. For were it not so placed all prehension would be as impossible, as were there no hand at all. For the pressure of this digit is applied from [15] below upwards, while the rest act from above downwards; an arrangement which is essential, if the grasp is to be firm and hold like a tight clamp. As for the shortness of this digit, the object is to increase its strength, so that it may be able, though but one, to counterbalance the other four.19 Moreover, were it long it would be of no use. (The finger which stands at the end is small, while the central one of all is long, like a centre oar in a ship. This is rightly so; for it is mainly by the central part of the [20] encircling grasp that a tool must be held when put to use.) And for this reason it is called the great finger, though it is small, because the others are pretty well useless without it.

No less skilfully contrived are the nails. For, while in man these serve simply as [25] coverings to protect the tips of the fingers, in other animals they are also used for active purposes.

The arms in man and the fore limbs in quadrupeds bend in contrary directions, this difference having reference to the conveying of food and to the other offices which belong to these parts. For quadrupeds must of necessity bend their anterior limbs inwards that they may serve in locomotion; for they use them as feet. Not but what even among quadrupeds there is at any rate a tendency for such as are [30] polydactylous to use their forefeet not only for locomotion but as hands. And they are in fact so used, as any one may see. For these animals seize hold of objects, and also repel assailants with their anterior limbs; whereas quadrupeds with solid hoofs [688a1] use their hind legs for this latter purpose. For their fore limbs are not analogous to the elbows and hands of man.

It is this which explains why in some of the polydactylous quadrupeds, such as wolves, lions, dogs, and leopards, there are actually five digits on each forefoot, though there are only four on each hind one. For the fifth digit of the foot [5] corresponds to the fifth digit of the hand, and like it is called the big one. It is true that in the smaller polydactylous quadrupeds the hind feet also have each five toes. But this is because these animals are creepers; and the increased number of nails serves to give them a tighter grip, and so enables them to creep up steep places with [10] greater facility, or even to run head downwards.

In man between the arms, and in other animals between the forelegs, lies what is called the chest. This in man is broad, as one might expect; for as the arms are set laterally on the body, they offer no impediment to such expansion in this part. But in quadrupeds the chest is narrow, owing to the legs having to be extended in a forward [15] direction in progression and locomotion.

For this reason the breasts of quadrupeds are never placed on the chest. But in the human body there is ample space in this part; moreover, the heart and neighbouring organs require protection, and for these reasons this part is fleshy and [20] the breasts are placed upon it separately, being themselves of a fleshy substance in the male for the reason just stated; while in the female, nature, in accordance with what we say is her frequent practice, makes them minister to an additional function, employing them as a store-place of nutriment for the offspring. The human breasts [25] are two in number, in accordance with the division of the body into two halves, a right and a left. They are somewhat firmer and divided, because the ribs in this region are joined together and because their presence is not burdensome. In other animals it is impossible for the breasts to be placed on the chest between the [30] forelegs, for they would interfere with locomotion; they are therefore disposed of in a variety of ways. Thus in such animals as produce but few at a birth, whether horned quadrupeds or those with solid hoofs, the breasts are placed in the region of the thighs, and are two in number, while in such as produce litters, or such as are polydactylous, they are either numerous and placed laterally on the belly, as in pigs and dogs, or are only two in number, being set, however, in the centre of the [688b1] abdomen, as in the case in the lion. The explanation of this is not that the lion produces few at a birth, for sometimes it has more than two cubs at a time, but is to be found in the fact that this animal has no plentiful supply of milk. For, being a flesh-eater, it gets food at but rare intervals, and such nourishment as it obtains is all expended on the growth of its body.

In the elephant also there are but two breasts which are placed under the pits [5] of the forelimbs. The breasts are not more than two, because this animal has only a single young one at a birth; and they are not placed in the region of the thighs, because they never occupy that position in any polydactylous animal such as this. Lastly, they are placed above, close to the armpits, because this is the position of the [10] foremost breasts in all animals whose breasts are numerous, and they give the most milk. Evidence of this is furnished by the sow. For she always presents these foremost teats to the first-born of her litter. A single young one is of course a first-born, and so such animals as only produce a single young one must have these first breasts, and the first breasts are those under the armpits. This, then, is the [15] reason why the elephant has but two breasts, and why they are so placed. But, in such animals as have litters of young, the teats are disposed about the belly; the reason being that more teats are required by those that will have more young to nourish. Now it is impossible that these should be set transversely in rows of more than two, one, that is, for each side of the body, the right and the left; they must [20] therefore be placed lengthways, and the only place where there is sufficient length for this is the region between the front and hind legs. As to the animals that are not polydactylous but produce few at a birth, or have horns, their breasts are placed in the region of the thighs. The horse, the ass, the camel are examples; all of which bear but a single young one at a time, and of which the two former have solid hoofs, while in the last the hoof is cloven. As still further examples may be mentioned the [25] deer, the ox, the goat, and all other similar animals.

The explanation is that in these animals growth takes place in an upward direction; so that there must be an abundant collection of residual matter and of blood in the lower region, that is to say in the neighbourhood of the orifices for efflux, and here therefore nature has placed the breasts. For the place in which the [30] nutriment is set in motion must also be the place whence nutriment can be derived by them. In man there are breasts in the male as well as in the female; but some of the males of other animals are without them. Such, for instance, is the case with horses, some stallions being destitute of these parts, while others that resemble their dams have them. Thus much then concerning the breasts.

Next after the chest comes the region of the belly, which is left unenclosed by [689a1] the ribs for a reason which has already been given; namely that there may be no impediment to the swelling which necessarily occurs in the food as it gets heated, not to the expansion of the womb in pregnancy.

At the extreme end of what is called the trunk are the parts concerned in the [5] evacuation of the solid and of the fluid residue. In all sanguineous animals with some few exceptions, and in all Vivipara without any exception at all, the same part which serves for the evacuation of the fluid residue is also made by nature to serve in sexual congress, and this alike in male and female. For the semen is a kind of fluid [10] and residual matter. (The proof of this will be given hereafter, but for the present let it be taken for granted.) The like holds good of the menstrual fluid in women, and of the part where they emit semen. This also, however, is a matter of which a more accurate account will be given hereafter. For the present let it be simply stated as a fact, that the menstrual fluids of the female are also residual matter. Both of them, moreover, being fluid, it is only natural that things which are alike should be [15] discharged into the same parts. Of the internal structure of these parts, and of the differences which exist between the parts concerned with semen and the parts concerned with conception, a clear account is given in the History of Animals and in the Anatomies. Moreover, I shall have to speak of them later in the work On [20] Generation. As regards, however, the external shape of these parts, it is plain enough that they are adapted to their operations, as indeed of necessity they must be. There are, however, differences in the male organ corresponding to differences in the body generally. For all animals are not of an equally sinewy nature. This organ, again, is the only one that, independently of any morbid change, admits of augmentation and of diminution of bulk. The former condition is of service in [25] copulation, while the other is required for the advantage of the body at large. For, were the organ constantly in the former condition, it would be an incumbrance. The organ therefore has been formed of such constituents as will admit of either state. For it is partly sinewy, partly cartilaginous, and thus is enabled either to contract or [30] to become extended, and is capable of admitting air.

All female quadrupeds are retromingent, because the position of the parts which this implies is useful to them in the act of copulation. This is the case with only some few males, such as the lynx, the lion, the camel, and the hare. No quadruped with a solid hoof is retromingent. [689b1]

The posterior portion of the body and the parts about the legs are peculiar in man as compared with quadrupeds. Nearly all these latter have a tail, and this whether they are viviparous or oviparous. For, even if the tail be of no great size, yet they have a kind of stump as at any rate a small representative of it. But man is [5] tail-less. He has, however, buttocks, which exist in none of the quadrupeds. His legs also are fleshy (as too are his thighs and calves); while the legs in all other animals that have any, whether viviparous or not, are fleshless, being made of sinew and bone and spinous substance. For all these differences there is, so to say, one common [10] explanation, and this is that of all animals man alone stands erect. It was to facilitate the maintenance of this position that nature made his upper parts light, taking away some of their corporeal substance, and using it to increase the weight of the parts below, so that the buttocks, the thighs, and the calves of the legs were all [15] made fleshy. The character which she thus gave to the buttocks renders them at the same time useful in resting the body. For standing causes no fatigue to quadrupeds, and even the long continuance of this posture produces in them no weariness; for they are supported the whole time by four props, which is much as though they were lying down. But to man it is no easy task to remain for any length of time on his feet, [20] his body demanding rest in a sitting position. This, then, is the reason why man has buttocks and fleshy legs; and the presence of these fleshy parts explains why he has no tail. For the nutriment which would otherwise go to the tail is used up in the production of these parts, while at the same time the existence of buttocks does away with the necessity of a tail. But in quadrupeds and other animals the reverse [25] obtains. For they are of dwarf-like form, so that all the pressure of their weight and corporeal substance is on their upper part, and is withdrawn from the parts below. On this account they are without buttocks and have hard legs. In order, however, to cover and protect that part which serves for the evacuation of excrement, nature has [30] given them a tail of some kind or other, subtracting for the purpose some of the nutriment which would otherwise go to the legs. Intermediate in shape between man and quadrupeds is the ape, belonging therefore to neither or to both, and having on this account neither tail nor buttocks; no tail in its character of biped, no [690a1] buttocks in its character of quadruped. There is a great diversity of so-called tails; and this organ like others is sometimes used by nature for by-purposes, being made to serve not only as a covering and protection to the fundament, but also for other uses and advantages of its possessor.

[5] There are differences in the feet of quadrupeds. For in some of these animals there is a solid hoof, and in others a hoof cloven into two, and again in others a foot divided into many parts.

The hoof is solid when the body is large and the earthy matter present in great abundance; in which case the earth, instead of forming teeth and horns, is separated [10] in the character of a nail, and being very abundant forms one continuous nail, that is a hoof, in place of several. This explains why these animals, as a rule, have no huckle-bones; a second reason being that the presence of such a bone in the joint of the hind leg somewhat impedes its free motion. For extension and flexion can be made more rapidly in parts that have but one angle than in parts that have several. But the presence of a huckle-bone, as a connecting bolt is the introduction as it were [15] of a new limb between the two. Such an addition adds to the weight of the foot, but renders the act of progression more secure. Thus it is that in such animals as have a huckle-bone, it is only in the posterior and not in the anterior limbs that this bone is found. For the anterior limbs, moving as they do in advance of the others, require to be light and capable of ready flexion, whereas firmness and extensibility are what [20] are wanted in the hind limbs. Moreover, a huckle-bone adds weight to the blow of a limb, and so renders it a suitable weapon of defence; and these animals all use their hind legs to protect themselves, kicking out against anything which annoys them. In the cloven-hoofed quadrupeds the lighter character of the hind legs admits of there being a huckle-bone; and the presence of the huckle-bone prevents them from having a solid hoof, the bony substance remaining in the joint, and therefore being deficient in the foot. As to the polydactylous quadrupeds, none of them have [25] huckle-bones. For if they had they would not be polydactylous, but the divisions of the foot would only extend to that amount of its breadth which was covered by the huckle-bone. Thus it is that most of the animals that have huckle-bones are cloven-hoofed.

Of all animals man has the largest foot in proportion to the size of the body. This is only what might be expected. For seeing that he is the only animal that [30] stands erect, the two feet which are going to bear all the weight of the body must be both long and broad. Equally intelligible is it that the proportion between the size of the fingers and that of the whole hand should be inverted in the case of the toes and feet. For the function of the hands is to take hold of objects and retain them by [690b1] pressure; so that the fingers require to be long. For it is by its flexed portion that the hand grasps an object. But the function of the feet is to enable us to stand securely, and for this the undivided part of the foot requires to be of larger size than the toes. And it is better for the extremity to be divided than to be undivided. For in an undivided foot disease of any one part would extend to the whole organ; whereas, if [5] the foot be divided into separate digits, there is not an equal liability to such an occurrence. The digits, again, by being short would be less liable to injury. For these reasons the feet in man are many-toed, while the separate digits are of no great length. The toes, finally, are furnished with nails for the same reason as are the fingers, namely because the tips are weak and therefore require special protection. [10]

11 · We have now done with practically all the sanguineous animals that live on land and bring forth their young alive. Of the oviparous Sanguinea, some have four feet, while others have none. The latter form a single genus, namely the serpents; and why these are footless has been already explained in the remarks On [15] the Progression of Animals. But in other respects serpents resemble the oviparous quadrupeds in their conformation.

In all these animals there is a head with its component parts; its presence being determined by the same causes as obtain in the case of other sanguineous animals; and in all, with the single exception of the river crocodile, there is a tongue inside the [20] mouth. In this one exception there would seem to be no actual tongue, but merely a space left vacant for it. The reason is that a crocodile is in a way a land-animal and a water-animal combined. In its character of land-animal it has a space for a tongue; but in its character of water-animal it is without the tongue itself. For in some fishes, as has already been mentioned, there is no appearance whatsoever of a [25] tongue, unless the mouth be stretched open very widely indeed; while in others it is indistinctly separated from the rest of the mouth. The reason for this is that a tongue would be of but little service to such animals, seeing that they are unable to chew their food or to taste it beforehand, the pleasurable sensations they derive from it occurring during swallowing. For it is in their passage down the gullet that solid edibles cause enjoyment, while it is by the tongue that the savour of fluids is [30] perceived. Thus it is during swallowing that the oiliness, the heat, and other such qualities of food are recognized. Now the Vivipara too have this power of perception (and in fact the satisfaction from most solid edibles and dainties is derived almost entirely from the dilatation of the oesophagus during swallowing—that is why the [691a1] same animals are not intemperate both with regard to tasty drinks and with regard to dainty foods); but while other animals have in addition the sensation of taste, [5] tongueless animals lack it and have the other sensation only.

In some oviparous quadrupeds, namely in lizards, the tongue is bifid, as also it is in serpents, and its terminal divisions are of hair-like fineness, as has already been described. (Seals also have a forked tongue.) This is why all these animals are fond of dainty food. The teeth in the four-footed Ovipara are of the saw-like kind, like the [10] teeth of fishes. The organs of all the senses are present and resemble those of other animals. Thus there are nostrils for smell, eyes for vision, and ears for hearing. The latter organs, however, do not project from the sides of the head, but consist simply [15] of the duct, as also is the case in birds. This is due in both cases to the hardness of the integument; birds having their bodies covered with feathers, and these oviparous quadrupeds with horny plates. These plates are equivalent to scales, but of a harder character. This is manifest in tortoises and river crocodiles, and also in the large serpents. For here the plates become stronger than the bones, being of the same substance as these.

[20] These animals have no upper eyelid, but close the eye with the lower lid. In this they resemble birds, and the reason is the same as was assigned in their case. Among birds there are some that also blink by means of a membrane which comes from the corner of the eye. But none of the oviparous quadrupeds blink; for their [25] eyes are harder than those of birds. The reason for this is that keen vision is of very considerable service to birds, flying as they do in the air, whereas it would be of comparatively small use to the oviparous quadrupeds, seeing that they all live in holes.

Of the two separate portions which constitute the head, namely the upper part and the lower jaw, the latter in man and in the viviparous quadrupeds moves not [30] only upwards and downwards, but also from side to side; while in fishes and birds and oviparous quadrupeds, the only movement is up and down. The reason is that [691b1] this latter movement is the one required in biting and dividing food, while the lateral movement serves to reduce substances to a pulp. To such animals, therefore, as have molars this lateral motion is of service; but to those animals that have none it would be quite useless, and they are therefore invariably without it. For nature never [5] makes anything that is superfluous. While in all other animals it is the lower jaw that is movable, in the river crocodile it is exceptionally the upper. This is because the feet in this creature are so excessively small as to be useless for seizing and holding prey; on which account nature has given it a mouth that can serve for these [10] purposes in their stead. For that direction of motion which will give the greater force to a blow will be the more serviceable one in holding or in seizing prey; and a blow from above is always more forcible than one from below. Seeing, then, that both the prehension and the mastication of food are offices of the mouth, and that [15] the former of these two is the more essential in an animal that has neither hands nor suitably formed feet, these crocodiles will derive greater benefit from a motion of the upper jaw than from a motion of the lower jaw. The same considerations explain why crabs also move the upper division of each claw and not the lower. For their claws are substitutes for hands, and so require to be suitable for the prehension of [20] food, and not for its division; for such division and biting is the office of teeth. In crabs, then, and in such other animals as are able to seize their food in a leisurely manner, inasmuch as their mouth is not called on to perform its office while they are still in the water, the two functions are assigned to different parts, prehension to the [25] hands or feet, biting and division of food to the mouth. But in crocodiles the mouth has been so framed by nature as to serve both purposes, the jaws being made to move in the manner just described.

Another part present in all these animals is a neck, this being the consequence of their having a lung. For the windpipe by which the air is admitted to the lung is of some length. Since the portion between the head and the shoulders is called the neck, a serpent can scarcely be said with the same right as the rest of these animals to have a neck, but only to have something analogous to that part of the body—if, [30] indeed, the neck must be determined by the limits just stated. It is a peculiarity of serpents, as compared with other animals allied to them, that they are able to turn [692a1] their head backwards without stirring the rest of the body. The reason of this is that a serpent, like an insect, has a body that admits of being curled up, its vertebrae being cartilaginous and easily bent. The faculty in question belongs then to serpents as a necessary consequence of this cause; but it is for the sake of their good too—for [5] it enables them to guard against attacks from behind. For their body, owing to its length and the absence of feet, is ill-suited for turning round and protecting the hinder parts; and merely to lift the head, without the power of turning it round, would be of no use whatsoever.

The animals with which we are dealing have, moreover, a part which corresponds to the chest; but neither here nor elsewhere in their body have they any [10] breasts, as neither has any bird or fish. This is a consequence of their having no milk; for a breast is a receptacle for milk and, as it were, a vessel to contain it. This absence of milk is not peculiar to these animals, but is common to all such as are not internally viviparous. For all such produce eggs, and the nutriment which in Vivipara has the character of milk is in them engendered in the egg. Of all this, however, a clearer account will be given in the treatise On Generation. As to the [15] mode in which the legs bend, a general account, in which all animals are considered, has already been given in the work on Progression. These animals also have a tail, larger in some of them, smaller in others, and the reason for this has been stated in general terms in an earlier passage.

Of all oviparous animals that live on land there is none so lean as the [20] chamaeleon. For there is none that has so little blood. The explanation of this is to be found in the psychical temperament of the creature. For it is of a timid nature—hence its many changes of appearance. But fear is a refrigeration, and results from deficiency of natural heat and scantiness of blood.

We have now done with such sanguineous animals as are quadrupeds and also [692b1] such as are footless, and have stated with sufficient completeness what external parts they possess, and for what reasons they have them.

12 · The differences of birds compared one with another are differences of magnitude, and of the greater or smaller development of parts. Thus some have long [5] legs, others short legs; some have a broad tongue, others a narrow tongue; and so on with the other parts. There are few of their parts that differ, taking birds by themselves. But when birds are compared with other animals the parts present differences of form also.

Birds, then, are feathered, and this is a character common to them all and [10] peculiar to them. For the parts of animals are covered in some cases with hair, in others with scales, in others with scaly plates; but birds have feathers. Their feathers, too, are split and distinct in kind from the undivided feathers of insects; for the bird’s feather is divided, these are not; the bird’s feather has a shaft, these have none.

[15] A second strange peculiarity which distinguishes birds from all other animals is their beak. For as in elephants the nostril serves in place of hands, and as in some insects the tongue serves in place of mouth, so in birds there is a beak, which, being bony, serves in place of teeth and lips. Their organs of sense have already been considered.

[20] All birds have a neck naturally extending from the body; and the purpose of this neck is the same as in such other animals as have one. This neck in some birds is long, in others short; its length, as a general rule, being pretty nearly determined by that of the legs. For long-legged birds have a long neck, short-legged birds a short one, to which rule, however, the web-footed birds form an exception. For to a bird [693a1] perched up on long legs a short neck would be of no use whatsoever in collecting food from the ground; and equally useless would be a long neck, if the legs were short. Such birds, again, as are carnivorous would find length in this part interfered [5] greatly with their habits of life. For a long neck is weak, and it is on their superior strength that carnivorous birds depend for their subsistence. No bird, therefore, that has talons ever has an elongated neck. In web-footed birds, however, and in those other birds belonging to the same class, whose toes though actually separate are shaped like a snub nose, the neck is elongated, so as to be suitable for collecting [10] food from the water; while the legs are short, so as to serve in swimming.

The beaks of birds also vary with their modes of life. For in some the beak is straight, in others crooked; straight, in those who use it merely for eating; crooked, in those that live on raw flesh. For a crooked beak is an advantage in fighting; and these birds must, of course, get their food from the bodies of other animals, and in [15] most cases by violence. In such birds, again, as live in marshes and are herbivorous the beak is broad and flat, this form being best suited for digging and cropping, and for pulling up plants. In some of these marsh birds, however, the beak is elongated, as too is the neck, the reason for this being that the bird gets its food from some depth below the surface. For most birds of this kind, and most of those whose feet [20] are webbed, either in their entirety or each part separately, live by preying on some of the smaller animals that are to be found in water, and their neck serves as a fishing-rod, the beak representing the line and hook.

The upper and under sides of the body, that is of what in quadrupeds is called the trunk, present in birds one unbroken surface, and they have no arms or forelegs [693b1] attached to it, but in their stead wings, which are a distinctive peculiarity of these animals; and that is why the ends of the wings lie on the back in the place of a shoulder-blade.

The legs are two in number, as in man; not however, as in man, bent outwards, [5] but bent inwards like the legs of a quadruped. The wings are bent like the forelegs of a quadruped, having their convexity turned outwards. That the feet should be two in number is a matter of necessity. For a bird is essentially a sanguineous animal, and at the same time a winged animal; and no sanguineous animal has more than four points for motion. In birds, then, as in those other sanguineous animals that live and move upon the ground, the limbs attached to the trunk are four in number. But, while in all the rest these four limbs consist of a pair of arms and a pair of legs, or of [10] four legs as in quadrupeds, in birds the arms or forelegs are replaced by a pair of wings, and this is their distinctive character. For it is part of the substance of a bird that it shall be able to fly; and it is by the extension of wings that this is made possible. Of all arrangements, then, the only possible, and so the necessary, one is that birds shall have two feet; for this with the wings will give them four points for [15] motion. The breast in all birds is sharp-edged, and fleshy. The sharp edge is to minister to flight, for broad surfaces move with considerable difficulty, owing to the large quantity of air which they have to displace; while the fleshy character acts as a protection, for the breast, owing to its form, would be weak, were it not amply covered.

Below the breast lies the belly, extending, as in quadrupeds and in man, to the vent and to the place where the legs are jointed to the trunk. [20]

Such, then, are the parts which lie between the wings and the legs. Birds like all other animals, whether produced viviparously or from eggs, have an umbilicus during their development, but, when the bird has attained to fuller growth, no signs of this remain visible. The cause of this is plainly to be seen during the process of development; for in birds the umbilical cord unites with the intestine, and is not a [25] portion of the blood vessels as is the case in viviparous animals.

Some birds, again, are well adapted for flight, their wings being large and strong. Such, for instance, are those that have talons and live on flesh. For their [694a1] mode of life renders the power of flight a necessity, and it is on this account that their feathers are so abundant and their wings so large. Besides these, however, there are also other genera of birds that can fly well; all those, namely, that depend [5] on speed for security, or that are of migratory habits. On the other hand, some kinds of birds have heavy bodies and are not constructed for flight. These are birds that are frugivorous and live on the ground, or that are able to swim and get their living in watery places. In those that have talons the body, without the wings, is small; for the nutriment is consumed in the production of these wings, and of the weapons and defensive appliances; whereas in birds that are not made for flight the contrary [10] obtains, and the body is bulky and so of heavy weight. In some of these heavy-bodied birds the legs are furnished with what are called spurs, which replace the wings as a means of defence. Spurs and talons never co-exist in the same bird. For nature never makes anything superfluous; and if a bird can fly, and has talons, [15] it has no use for spurs; for these are weapons for fighting on the ground, and on this account belong to certain heavy-bodied birds. These latter, again, would find the possession of talons not only useless but actually injurious; for the claws would stick into the ground and interfere with progression. This is the reason why all birds with talons walk so badly, and why they never settle upon rocks. For the character of [20] their claws is ill-suited for either action.

All this is the necessary consequence of the process of development. For the earthy matter in the body issuing from it is converted into parts that are useful as weapons. That which flows upwards gives hardness or size to the beak; and, should [25] any flow downwards, it either forms spurs upon the legs or gives size and strength to the claws upon the feet. But it does not at one and the same time produce both these results, one in the legs, the other in the claws; for such a dispersion of this residual matter would destroy all its efficiency. In other birds this earthy residue furnishes [694b1] the legs with the material for their elongation; or sometimes, in place of this, fills up the interspaces between the toes. Thus it is a matter of necessity that such birds as swim shall either be actually web-footed, or shall have a kind of broad blade-like [5] margin running along the whole length of each distinct toe. The forms, then, of these feet are the necessary results of the causes that have been mentioned. Yet at the same time they are intended for the animal’s advantage. For they are in harmony with the mode of life of these birds, who, living on the water, where their wings are useless, require that their feet shall be such as to serve in swimming. For [10] these feet are so developed as to resemble the oars of a boat, or the fins of a fish; and if the fins of the one or the webbing of the other is destroyed, they can no longer swim.

In some birds the legs are very long, the cause of this being that they inhabit marshes—and nature makes the organs for the function, and not the function for [15] the organs. It is, then, because these birds are not meant for swimming that their feet are without webs, and it is because they live on ground that gives way under the foot that their legs and toes are elongated, and that these latter in most of them have an extra number of joints. Again, though all birds have the same material composition, they are not all made for flight; and in these, therefore, the nutriment [20] that should go to their tail-feathers is spent on the legs and used to increase their size. This is the reason why these birds when they fly make use of their legs as a tail, stretching them out behind, and so rendering them serviceable, whereas in any other position they would be simply an impediment.

In other birds, where the legs are short, these are held close against the belly [25] during flight. In some cases this is merely to keep the feet out of the way, but in birds that have talons the position has a further purpose, being the one best suited for rapine. Birds that have a long and a thick neck keep it stretched out during flight; but those whose neck though long is slender fly with it coiled up. For in this position it is protected, and less likely to get broken, should the bird fly against any obstacle.

[695a1] In all birds there is an ischium, but in such a way that it would scarcely be taken for one, but rather for a second thigh-bone because of its length; for it extends as far as to the middle of the belly. The reason for this is that the bird is a biped, and yet is unable to stand erect. For if its ischium extended but a short way from the [5] fundament, and then immediately came the leg, as is the case in man and in quadrupeds, the bird would be unable to stand up at all. For while man stands erect, and while quadrupeds have their heavy bodies propped up in front by the forelegs, birds can neither stand erect owing to their dwarf-like shape, nor have anterior legs [10] to prop them up, these legs being replaced by wings. As a remedy for this nature has given them a long ischium, and brought it to the centre of the body, fixing it firmly; and she has placed the legs under this, so that the weight on either side may be equally balanced, and standing or progression rendered possible. Such then is the reason why a bird, though it is a biped, does not stand erect. The reason why its legs are destitute of flesh is the same as in the case of quadrupeds, about which we have already spoken.

In all birds alike, whether web-footed or not, the number of toes in each foot is [15] four. For the Libyan ostrich may be disregarded for the present, and its cloven hoof and other discrepancies of structure as compared with the tribe of birds will be considered further on. Of these four toes three are in front, while the fourth points backwards, serving as a heel, to give steadiness. In the long-legged birds this fourth [20] toe is much shorter than the others, as is the case with the corncrake, but the number of their toes is not increased. The arrangement of the toes is such as has been described in all birds with the exception of the wryneck. Here only two of the toes are in front, the other two behind; and the reason for this is that the body of the wryneck is not inclined forward so much as that of other birds. All birds have [25] testicles; but they are inside the body. The reason for this will be given in the treatise on the Generation of Animals.

13 · Thus then are fashioned the parts of birds. But in fishes a still further [695b1] stunting has occurred in the external parts. For here, for reasons already given, there are neither legs nor hands nor wings, the whole body from head to tail [5] presenting one unbroken surface. This tail differs in different fishes, in some approximating in character to the fins,20 while in some of the flat kinds, it is spinous and elongated, because the material which should have gone to the tail has been diverted thence and used to increase the breadth of the body. Such, for instance, is the case with the torpedos, the sting-rays, and whatever other Selachia there may be of like nature. In such fishes, then, the tail is spinous and long; while in some others [10] it is short and fleshy, for the same reason which makes it spinous and long in the torpedo. For to be short and fleshy comes to the same thing as to be long and less amply furnished with flesh.

The opposite has occurred in the fishing-frog; for here the anterior and broad part of the body is not of a fleshy character, and so all the fleshy substance which [15] has been thence diverted has been placed by nature in the tail and hinder portion of the body.

In fishes there are no limbs attached to the body. For in accordance with their essential substance they are swimming animals; and nature never makes anything superfluous or in vain. Now fish are sanguineous in their substance; and since they [20] are made for swimming they have fins, and as they are not made for walking they are without feet; for feet are attached to the body that they may be of use in progression on land. Moreover, fishes cannot have feet, or any other similar limbs, as well as four fins; for they are sanguineous animals. The cordylus, though it has [25] gills, has feet, for it has no fins but has its tail flattened out and loose in texture.

Fishes, unless, like the ray and the sting-ray they are broad and flat, have four [696a1] fins, two on the upper and two on the under side of the body; and no fish ever has more than these. For, if it had, it would be a bloodless animal.

The upper pair of fins is present in nearly all fishes, but not so the under pair; for these are wanting in some of those fishes that have long thick bodies, such as the [5] eel, the conger, and a certain kind of mullet that is found in the lake at Siphae. When the body is still more elongated, and resembles that of a serpent as is the case in the muraena, there are absolutely no fins at all; and locomotion is effected by the flexures of the body, the water being put to the same use by these fins as is the ground by serpents. For serpents swim in water exactly in the same way as they [10] glide on the ground. The reason for these serpent-like fishes being without fins is the same as that which causes serpents to be without feet; and what this is has been already stated in the works on the Progression and the Movement of Animals. The reason was this. If the points of motion were four, motion would be effected under difficulties; for either the two pairs of fins would be close to each other, in which case motion would scarcely be possible, or they would be at a very considerable [15] distance apart, in which case the long interval between them would be just as great an evil. On the other hand, to have more than four such motor points would convert the fishes into bloodless animals. A similar explanation applies to the case of those fishes that have only two fins. For here again the body is of great length and like that of a serpent, and its undulations do the office of the two missing fins. It is owing to this that such fishes can even crawl on dry ground, and can live there for a [20] considerable time; and some do not begin to gasp at once, while others, whose nature is akin to that of land-animals, are still less affected. In such fishes as have but two fins it is the upper pair that is present, excepting when the flat broad shape of the body prevents this. The fins in such cases are placed at the head, because in this region there is no elongation, which might serve in the absence of fins as a [25] means of locomotion; whereas in the direction of the tail there is a considerable lengthening out in fishes of this conformation. As for the rays and the like, they use the marginal part of their flattened bodies in place of fins for swimming.

Fish which are not so flat, e.g. the torpedo and the fishing-frog, have fins: the upper pair are placed further back because of the flatness of the fore parts, and the under pair are placed close to the head (for the flatness does not prevent it from [30] moving), while to compensate for this advancement they are smaller than the upper ones. In the torpedo two fins are placed on the tail, and the fish uses the broad expansion of its body to supply the place of the other two, each lateral half of its circumference serving the office of a fin.

The head, with its several parts, as also the organs of sense, have already come under consideration.

There is one peculiarity which distinguishes fishes from all other sanguineous [696b1] animals, namely, the possession of gills. Why they have these organs has been set forth in the treatise on Respiration. These gills are in most fishes covered by opercula, but in the Selachia there are no such coverings. For an operculum requires [5] fish-spine for its formation, and in other fishes the skeleton is made of this substance, whereas in the Selachia it is invariably formed of cartilage. Again, while the motions of spinous fishes are rapid, those of the Selachia are sluggish, inasmuch as they have neither fish-spine nor sinew; but an operculum requires rapidity of motion, seeing that the office of the gills is to minister as it were to expiration. For this reason in Selachia the branchial orifices themselves effect their own closure, [10] and thus there is no need for an operculum to ensure its taking place with due rapidity. In some fishes the gills are numerous, in others few in number; in some again they are double, in others single. The last gill in most cases is single. For a detailed account of all this, reference must be made to the Anatomies and to the [15] History of Animals.

It is the abundance or the deficiency of the cardiac heat which determines the abundance or deficiency of the gills. For, the greater an animal’s heat, the more rapid and the more forcible does it require the branchial movement to be; and numerous and double gills act with more force and rapidity than such as are few and [20] single. Thus, too, it is that some fishes that have but few gills, and those of comparatively small efficacy, can live out of water for a considerable time; for in them there is no great demand for refrigeration. Such, for example, are the eel and all other fishes of serpent-like form.

Fishes also present diversities as regards the mouth. For in some this is placed in front, at the very extremity of the body, while in others, as the dolphin and the [25] Selachia, it is placed on the under surface; so that these fishes turn on the back in order to take their food. The purpose of nature in this was apparently not merely to provide a means of salvation for other animals, by allowing them opportunity of escape during the time lost in the act of turning—for all the fishes with this kind of mouth prey on living animals—but also to prevent these fishes from giving way too [30] much to their gluttonous ravening after food. For had they been able to seize their prey more easily than they do, they would soon have perished from over-repletion. An additional reason is that their snout is round and small, and therefore cannot admit of a wide opening.

Again, even when the mouth is not placed on the under surface, there are differences in the extent to which it can open. For in some cases it can gape widely, [697a1] while in others it is set at the point of a small tapering snout; the former being the case in carnivorous fishes, such as those with saw teeth, whose strength lies in their mouth, while the latter is its form in all such as are not carnivorous.

The skin is in some fishes covered with scales (the scale of a fish is a thin and [5] shiny film, and therefore easily becomes detached from the surface of the body). In others it is rough, as for instance in the angel-fish, the ray, and the like. Fewest of all are those whose skin is smooth. The Selachia have no scales, but a rough skin. This is explained by their cartilaginous skeleton. For the earthy material which has been thence diverted is expended by nature upon the skin.

No fish has testicles either externally or internally; as indeed have no footless [10] animals, among which of course are included the serpents. One and the same orifice serves both for the excrement and for the generative secretions, as is the case also in all other oviparous animals, quadrupeds included, inasmuch as they have no bladder and form no fluid excretion.

Such then are the characters which distinguish fishes from all other animals. [15] But dolphins and whales and all such Cetacea are without gills; and, having a lung, are provided with a blow-hole; for this serves them to discharge the sea-water which [20] has been taken into the mouth. For, feeding as they do in the water, they cannot but let this fluid enter into their mouth, and, having let it in, they must of necessity let it out again. Gills are useful here, as has been explained in the treatise on Respiration, to such animals as do not breathe; for no animal can possibly possess gills and at the same time be a respiratory animal. In order, therefore, that these Cetacea may discharge the water, they are provided with a blow-hole. This is placed in front of [25] the brain; for otherwise it would have cut off the brain from the spine. The reason for these animals having a lung and breathing, is that animals of large size require more heat to enable them to move. A lung, therefore, is placed within their body, and is fully supplied with blood-heat. These creatures are after a fashion land and [30] water animals in one. For so far as they are inhalers of air they resemble land-animals, while they resemble water-animals in having no feet and in deriving [697b1] their food from the sea. So also seals and bats are ambivalent, the former between land and water animals, and the latter between animals that live on the ground and animals that fly; and so they belong to both kinds or to neither. For seals, if looked [5] on as water-animals, are yet found to have fins. For their hind feet are exactly like the fins of fishes; and their teeth also are sharp and saw-like as in fishes. Bats again, if regarded as winged animals, have feet; and, if regarded as quadrupeds, are without them. So also they have neither the tail of a quadruped nor the tail of a bird; [10] no quadruped’s tail, because they are winged animals; no bird’s tail, because they are terrestrial. This absence of tail is the result of necessity. For they are skin-winged; but no animal, unless it has barbed feathers, has the tail of a bird; for a bird’s tail is composed of such feathers. As for a quadruped’s tail, it would be an actual impediment, if present among the feathers.

14 · Much the same may be said also of the Libyan ostrich. For it has some [15] of the characters of a bird, some of the characters of a quadruped. It differs from a quadruped in being feathered; and from a bird in being unable to soar aloft, and in having feathers that resemble hair and are useless for flight. Again, it agrees with quadrupeds in having upper eyelashes, and the parts about the head and the upper [20] portion of the neck are bare—so that its eyelashes are more hairy; and it agrees with birds in being feathered in all the parts posterior to these. Further, it resembles a bird in being a biped, and a quadruped in having a cloven hoof; for it has hoofs and not toes. The explanation of these peculiarities is to be found in its bulk, which is that of a quadruped rather that of a bird. For speaking generally, a bird must [25] necessarily be of very small size. For a body of heavy bulk can with difficulty be raised into the air.

Thus much then as regards the parts of animals. We have discussed them all, and set forth the cause why each exists; and in do doing we have severally considered each group of animals. We must now pass on, and in due sequence must [30] next deal with the question of their generation.