220 CLASSIFICATION. [Chap. XIV. 



the water; but between the several members of the 

 whale family, the shape of the body and the fin-like 

 limbs offer characters exhibiting true affinity; for as 

 these parts are so nearly similar throughout the 

 whole family, we cannot doubt that they have 

 been inherited from a common ancestor. So it is with 

 fishes. 



Numerous cases could be given of striking resem- 

 blances in quite distinct beings between single parts or 

 organs, which have been adapted for the same functions. 

 A good instance is afforded by the close resemblance of 

 the jaws of the dog and Tasmanian wolf or Thylacinus, 

 — animals which are widely sundered in the natural 

 system. But this resemblance is confined to general ap- 

 pearance, as in the prominence of the canines, and in the 

 cutting shape of the molar teeth. For the teeth really 

 differ much: thus the dog has on each side of the upper 

 jaw four pre-molars and only two molars; whilst the 

 Thylacinus has three pre-molars and four molars. The 

 molars also differ much in the two animals in relative 

 size and structure. The adult dentition is preceded by 

 a widely different milk dentition. Any one may of 

 course deny that the teeth in either case have been 

 adapted for tearing flesh, through the natural selection 

 of successive variations; but if this be admitted in the 

 one case, it is unintelligible to me that it should be 

 denied in the other. I am glad to find that so high an 

 authority as Professor Flower has come to this same 

 conclusion. 



The extraordinary cases given in a former chapter, 

 of widely different fishes possessing electric organs, — of 



widely different insects possessing luminous organs, 



and of orchids and asclepiads having pollen-masses with 



