CLASSIFICATION. I"CHAr. XIV. 



Liunccus, misled by external appearances, actually classed an 

 homopterous insect as a moth. We see something of the same 

 kind even with our domestic varieties, as 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 turnip. The resemblance between the greyhound 

 and the racehorse 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 classifi- 

 cation, only in so far as they reveal descent, we can clearly under- 

 stand 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-relation- 

 ship. 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 members of 

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

 body and fin-like limbs are only analogical when whales are com- 

 pared 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 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 ; 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 dif- 

 ferent milk dentition. Any one may of course deny that the teeth 



