Chap. XIII. CLASSIFICATION. 427 



Geographical distribution may sometimes be brought 

 usefully into play in classing large and widely-distri- 

 buted genera, because all the species of the same genus, 

 inhabiting any distinct and isolated region, have in all 

 probability descended from the same parents. 



We can understand, on these views, the very im- 

 portant distinction between real affinities and analogical 

 or adaptive resemblances. Lamarck first called atten- 

 tion to this distinction, and he has been ably followed 

 by Macleay and others. The resemblance, in the shape 

 of the body and in the fin-like anterior limbs, between 

 the dugong, which is a pachydermatous animal, and the 

 whale, and between both these mammals and fishes, is 

 analogical. Amongst insects there are innumerable in- 

 stances : thus Linnaeus, misled by external appearances, 

 actually classed an homopterous insect as a moth. We 

 see something of the same kind even in our domestic 

 varieties, as in the thickened stems of the common and 

 Swedish turnip. The resemblance of the greyhound and 

 racehorse is hardly more fanciful than the analogies 

 winch have been drawn by some authors between very r 

 distinct animals. On my 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 character, 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 readily become adapted to similar 

 conditions, and thus assume a close external resem- 

 blance ; but such resemblances will not reveal — will 

 rather tend to conceal their blood-relationship to their 

 proper lines of descent. We can also understand the 

 apparent paradox, that the very same characters arc 

 analogical when one class or order is compared with 

 another, but give true affinities when the members of 



