EMBRYOGENY 



217 



(2) The speculative utilization of enibryological 

 evidence. 



Speculation has not been satisfied therewith. Each 

 ' rudiment ' which is met with in the embryogeny of 

 a present organic form should become a document of 

 the actual historical evolution of the type itself, at 

 least in such cases where the rudiment concerned 

 possesses a similarity to a really functional organ of an 

 adult type, even though a very distant one. A c germ 

 rudiment ' of a mammal embryo should no longer 

 point to a former free-living larval stage of the mammal 

 but to a true adult fish or a true tadpole. That is 

 maintained and believed. 1 



The most definite and most general formularization 

 of the enibryological argument is given by Hackel in 

 his ' biogenetic fundamental law/ 



In the best-known form it runs thus : ~ ' The onto- 

 genesis, or the development of the individual, is a short 

 recapitulation, controlled by the laws of inheritance 

 and adaptation, of the phylogenesis of the ancestors 

 which form the pedigree of the individual concerned/ 



1 It will perhaps be said that ' true ' is arbitrarily used ; ' fish-like ' 

 was only intended. To that it may be replied that the argument, in the 

 form in which we have presented it, is at least used by the Hackelites. 

 It should be really applied to lower classes for instance, Reptiles or Fish. 

 If the hypothetical fish-like ancestors of the Mammals were no fishes and 

 yet ' true,' then this application does not hold good. Furthermore Hackel 

 himself speaks quite simply of ' ancestors ' which may be ascertained by 

 his ' basal principle.' The acceptance, however, of ' fish-like ' ancestors 

 is not borne out by actual observation of facts, but in the meantime is 

 only based on a fish-like stage in the Mammalia already existent. 



2 Natiirliche Schopfungsgeschichte, p. 276. 



