132 The Science of Life. 



To assume that they are so involves us in inextricable 

 difficulties such as those, for instance, encountered in 

 the comparison of the Annelid gastrula with that of the 

 Chordates, or the comparison of the sexual and asexual 

 modes of development in Tunicates, Bryozoa, Worms, 

 and Ccelenterates." . . . " The relationship of the inner 

 and outer layers in the various forms of gastrulas must 

 be investigated, not only by determining" their relation- 

 ship to the adult body, but also by tracing out the cell- 

 lineage or cytogeny of the individual blastomeres from 

 the beginning of development. " 



In stating what is called "the evidence for evolution" 

 it is usual to refer to a series of embryological facts, 

 The influence sucn as ^ e occurrence of gill-clefts in the 

 of Evolution- embryos of higher Vertebrates, or the more 

 octnne. Qr | egg figh^i^g stages in the development 



of the frog; but it is erroneous to suppose that the 

 evolution-doctrine was, or can be, proved by the la- 

 borious induction of these and a thousand other facts. 

 Embryological facts are only evidences of evolution in 

 the sense that an acquaintance with them might possibly 

 suggest the evolution-idea to an acute and unprejudiced 

 mind, or in the sense that they are interesting and 

 somewhat obtrusively puzzling phenomena, of which the 

 evolution-theory furnishes a lucid interpretation, or in 

 the sense that none of them contradicts the idea at the 

 heart of the theory. There is no historical evidence 

 which even suggests that the evolution -theory was 

 arrived at by an inductive process, unless unconscious 

 induction be included in the phrase. An adequate 

 scientific doctrine should furnish an interpretation of 

 the facts, which is self-consistent, and consistent with 

 other doctrines, and this is what is claimed for the 

 doctrine of descent. Therefore it must be said, that 

 only a misunderstanding of the nature of scientific pro- 

 gress can explain the position of those who maintain 

 that there is a vicious circle in corroborating the evolu- 

 tion-doctrine from embryology, and at the same time 

 recognizing the evolution-doctrine as a suggestive influ- 

 ence in embryology. 



As an instance of the influence of the evolution- 



