EVOLUTIONISTS AND TRANSCENDENTALISTS 303 



or embryological, still continued in the same way as before, 

 and it was a point of subordinate importance that, under the 

 influence of the evolution-theory, these were considered to 

 represent real ancestral forms rather than purely abstract 

 figments of the intelligence. The law of Meckel-Serres was 

 revived in an altered shape as the law of the recapitulation of 

 phylogeny by ontogeny ; the natural system of classifica- 

 tion was passively inherited, and, by a petitio principii, taken 

 to represent the true course of evolution. It is true that the 

 attempt was made to substitute for the concept of homology 

 the purely genetic concept' of homogeny, but no inkling was 

 given of any possible method of recognising homogeny other 

 than the well-worn methods generally employed in the search 

 after homologies. 



There was a close spiritual affinity between the speculative 

 evolutionists and the transcendentalists. Both showed the 

 same subconscious craving for simplicist conceptions the 

 transcendentalists clung fast to the notion of the absolute 

 unity of type, of the ideal existence of the " one animal," and 

 the evolutionists did precisely the same thing when they 

 blindly and instinctively accepted the doctrine of the 

 monophyletic descent of all animals from one primeval form. 

 Geoffrey persisted in regarding Arthropods as being built on 

 the same plan as Vertebrates : Dohrn and Semper did 

 nothing different when they derived both groups from an 

 ancestor combining the main characters of both. The 

 determination to link together all the main phyla of the 

 animal kingdom and to force them all into a single mould 

 was common to evolutionary and pre-evolutionary trans- 

 cendentalists alike. 



From the fact that all Metazoa develop from an ovum 

 which is a simple cell, the evolutionists inferred that all 

 must have arisen from one primordial cell. From the fact 

 that the next step in development is the segmentation of 

 the ovum, they argued that the ancestral Metazoa came into 

 being through, the division of the primal Protozoon with 

 aggregation of the division-products. From the fact that a 

 gastrula stage is very commonly formed when segmentation 

 has been completed, they assumed that all germ-layered 

 animals were descended from an ancestral Gastraea. 



