THE INTERLUDE OF CANCER 125
was ultimately replaced by a corresponding, but differently developed, organ of the adult form (sexual generation). For a variety of reasons, into which space forbids entry here, it soon became clear to the writer that Kleinenberg’s doctrine was inadequate, and that, instead of a substitution of organs; there was in development in reality a substitution of organisms. The sexual organism replaced the asexual one. This was seen to be an alternation of generations, and as there was no homology or close likeness between the asexual generation or its organs and the sexual form or its organs, it was an antithetic alternation of generations.*
Now that we have the mention of the word “antithetic,” it may be permitted in passing to point out how Pasteur’s researches started in the antithesis of the two sorts of tartrate crystals: mine in that of two nervous systems in the life-history of a fish. Here we are dealing with anatomical antithesis ; later we shall come to recognize physiological antithesis—that of two ferments.
The tracing of the asexual generation in the backboned animals or vertebrata, from fishes to man, was not without its own special difficulties. These were due rather to expecting too much, and to failing at first to realize that the higher one ascended in the scale of life, the greater became the organization of the sexual form or generation, and the more insignificant the asexual one, until in the highest animals, the mammals and man, the asexual generation became reduced to the almost structureless chorion or trophoblast, as Professor A. W. Hubrecht named it in 1889. Many people, quite ignorant of all the embryological advances of recent years, appear to imagine that I not only introduced the
* See Appendix C, “The Metazoan Life-Cycle and Alternation of Generations.”