[en] [Gutenberg 47847] • Studies in the Theory of Descent, Volume I Wentworth Press
[en] [Gutenberg 47849] • Studies in the Theory of Descent (Volumes 1 and 2) Wentworth Press
[en] [Gutenberg 36003] • Degeneracy: Its Causes, Signs and Results Kessinger Publishing
[en] [Gutenberg 24800] • Darwin, and After Darwin, Volumes 1 and 3 / An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions Createspace Independent Publishing Platform
[en] [Gutenberg 49458] • An Examination of Weismannism Scholar's Choice
[de] [Gutenberg 50081] • Natur und Mensch / Sechs Abschnitte aus Werken von Ernst Haeckel Forgotten Books
[en] [Gutenberg 48288] • Inheritance of Characteristics in Domestic Fowl Palala Press