26 Heredity. 



the formation of the latter, for the branchial vessels are 

 soon, in part pulled down and destroyed, and in part pro- 

 foundly modified, in order to conform to the mammalian 

 type. 



Cases of this kind are almost universal, and the law 

 of resemblance between the early stages of higher ani- 

 mals and the adult condition of lower animals is a fun- 

 damental law of embryology. 



It is obvious that the hypothesis of evolution of a per- 

 fectly formed germ contained in the egg, is utterly ir- 

 reconcilable with this law, and we may therefore state 

 with confidence that this hypothesis is refuted by the 

 observed facts of embryology. 



"We must not forget, however, that there were other 

 less superficial forms of the evolution hypothesis, and 

 that these cannot be disproved so easily. 



Buffon, for instance, held that the embryo is built up 

 by the union of organic particles which are given off from 

 every part of the body of the parent, and which, assem- 

 bling in the sexual secretions, assume in the body of 

 the offspring positions like those which they occupied in 

 the parent. This is essentially an evolution hypothesis, 

 but it is logically complete, since it accounts for the pro- 

 duction of successive generations without the necessity 

 for assuming that they were all contained in embryo in 

 the body of a remote ancestor. Microscopic examina- 

 tion cannot overthrow this hypothesis, for a failure to 

 discover these organic particles with any particular mag- 

 nifying power does not, of course, disprove their existence 

 any more than a failure to see them without a microscope. 



Although Buffon's hypothesis does not account for the 

 fact that development is indirect in most cases, that the 

 egg does not build up the adult animal in the simplest 

 way, but takes a roundabout circuit, this fact is not 



