VI

PRECOCIOUS MATURITY, A METHOD OF SURVIVAL

NATURE IN HER insensate play with the possibilities of life has produced some abrupt novelties in the record by accelerating the fertilization and ripening of the ovum relatively to the other phases of the life cycle. We must bear in mind always in these questions that it is a complete life cycle we inherit and not some fixed adult form. And time and after time Nature has cut out an adult form from the record altogether, abolished it, and made some larval stage the sexually mature form.

At one early phase in the record, the Echinoderms, the starfish and so forth, with their radiant structure, were Lords of Creation. They had little or no powers of locomotion in their adult state, and many, like the crinoids, were rooted to the rocks. Among other radiant forms the Tunicata had reverted to the production of cellulose and were markedly vegetative in their habit of life. They discharged their fertilized eggs into the water and dissemination of these was greatly assisted by the development of accessory structures that stiffened the drifting larvae and gave an independent impetus to their movement. The backbone of these traveling emissions has been christened the notochord, and the new fore and aft forms of life of which it was the precursor, are called the Chordata, as opposed to the series of forms without notochords, the Starfish, Sea Urchins, Sea Cucumbers and so on, which had hitherto been Lords of Creation. The whole vast world of backboned animals, including ourselves, owes its existence to this freak of nature. There was no reason whatever in it. It happened so.

The notochord appears in the development of all vertebrated animals, but in all the higher forms it is invaded and superseded by cartilaginous or bony matter. It persists through life in the hag-fish and lampreys, and in the lamprey it comes to our tables.