414 ANALOGICAL RESEMBLANCES. 



in the strikingly similar shape of the body in the improved 

 breeds of the Chinese and common pig, which are descended 

 from distinct species ; and in the similarly thickened stems 

 of the common and specifically distinct Swedish tnrnip. The 

 resemblance between the greyhound and the race-horse is 

 hardly more fanciful than the analogies which have been 

 drawn by some authors between widely different animals. 



On the view of characters being of real importance for 

 classification, only in so far as they reveal descent, we can 

 clearly understand why analogical or adaptive characters, 

 although of the utmost importance to the welfare of the 

 being, are almost valueless to the systematist. For animals, 

 belonging to two most distinct lines of descent, may have 

 become adapted to similar conditions, and thus have assumed 

 a close external resemblance ; but such resemblances will not 

 reveal — will rather tend to conceal their blood-relationship. 

 We can thus also understand the apparent paradox, that the 

 very same characters are analogical when one group is com- 

 pared with another, but give true affinities when the mem- 

 bers of the same group are compared together: thus, the 

 shape of the body and fin-like limbs are only analogical when 

 whales are compared with fishes, being adaptations in both 

 classes for swimming through 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 resemblances 

 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 resem- 

 blance 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 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 



