CLASSIFICATION 229 



thus also understand tlie apparent paradox, that tlie very 

 same characters are analogical when one group is com- 

 pared with another, but give true affinities when the 

 members of the same group are compared together: thus, 

 the shape of the bod}^ and finlike limbs are only analogi- 

 cal when whales are compared with fishes, being adapta- 

 tions in both classes for swimming through the water; 

 but between the several members of the whale family, 

 the shape of the body and the finlike limbs offer char- 

 acters exhibitiag true aifiriifcy; for as thcHo parts arc 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 appearance, 

 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; while the Thyla- 

 cinus 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. An}^ 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 



