88 THE GENESIS OF SPECIES. [CHAP. 



in the vertebrates on the one hand, and in the mollusks on 

 the other, present us with residuary phenomena for which 

 " Natural Selection" alone is quite incompetent to account : 

 and that these same phenomena must therefore be con- 

 sidered as conclusive evidence for the action of some other 

 natural law or laws conditioning the simultaneous and 

 independent evolution of these harmonious and concordant 

 adaptations. 



Provided with this evidence, it may be now profitable to 

 enumerate other correspondences, which are not perhaps in 

 themselves inexplicable by " Natural Selection," but which 

 are more readily to be explained by the action of the 

 unknown law or laws referred to which action, as its 

 necessity has been demonstrated in one case, becomes 

 a priori probable in the others. 



Thus the great oceanic Mammalia the whales show 

 striking resemblances to those prodigious, extinct, marine 



SKELETON OF AN ICHTHYOSAURUS. 



reptiles, the Ichthyosauria, and this not only in structures 

 readily referable to similarity of habit, but in such matters 

 as greatly elongated premaxillary bones, together with the 

 concealment of certain bones of the skull by other cranial 

 bones. 



Again, the aerial mammals, the bats, resemble those flying 

 reptiles of the secondary epoch, the pterodactyles ; not only 

 to a certain extent in the breast-bone and mode of support- 



