HOMOLOGIES. 191 



together form either the radius and ulna or the tibia and 

 fibula, and so on. 



Now there is little doubt (from a priori considerations) 

 but that the special differentiation of the limb-bones of the 

 higher Vertebrates has been evolved from anterior condi- 

 tions existing in some fish-like form or other. But the 

 particular view advocated by the learned professor is open 

 to criticism. Thus, it may be objected against this view, 

 first, that it takes no account of the radial ossicle which 

 becomes so enormous in the mole ; secondly, that it does 

 not explain the extra series of ossicles which are formed on 

 the outer (radial or marginal) side of the paddle in the Ich- 

 thyosaurus ; and thirdly, and most importantly, that even if 

 this had been the way in which the limbs had been dif- 

 ferentiated, it would not be at all inconsistent with the 

 possession of an innate power of producing, and an innate 

 tendency to produce similar and symmetrical homological 

 resemblances. It would not be so because resemblances 

 of the kind are found to exist, which, on the Darwinian 

 theory, must be subsequent and secondary, not primitive 

 and ancestral. Thus we find in animals of the eft kind 





SKELETON OF AX ICHTHYOSAURUS. 



(certain amphibians), in which the tarsus is cartilaginous, 

 that the carpus is cartilaginous likewise. And we shall 

 see in cases of disease and of malformation what a ten- 

 dency there is to a similar affection of homologous parts. 



