"2. The hypertrophy or enlargement was probably [we should rather say _possibly_] primarily due to a change of station from herbs to trees, involving better air, a more equable temperature, perhaps a different and better food. "3. The enlarged and specialized tubercles developed more rapidly on certain segments than on others, especially the more prominent segments, because the nutritive fluids would tend more freely to supply parts most exposed to external stimuli. "4. The stimuli were in great part due to the visits of insects and birds, resulting in a mimicry of the spines and projections on the trees; the colors (lines and spots) were due to light or shade, with the general result of protective mimicry, or adaptation to tree-life. "5. As the result of some unknown factor some of the hypodermic cells at the base of the spines became in certain forms specialized so as to secrete a poisonous fluid. "6. After such primitive forms, members of different families, had become established on trees, a process of arboreal segregation or isolation would set in, and intercrossing with low-feeders would cease. "7. Heredity, or the unknown factors of which heredity is the result, would go on uninterruptedly, the result being a succession of generations perfectly adapted to arboreal life. "8. Finally the conservative agency of natural selection operates constantly, tending towards the preservation of the new varieties, species, and genera, and would not cease to act, in a given direction, so long as the environment remained the same. "9. Thus in order to account for the origin of a species, genus, family, order, or even a class, the first steps, causing the origination of variations, were in the beginning due to the primary (direct and indirect) factors of evolution (Neolamarckism), and the final stages were due to the secondary factors, segregation and natural selection (Darwinism)." From a late essay[225] we take the following extracts explaining our views: