Chap. XIII. ANALOGICAL RESEMBLANCES, 3S3 



be safely doiip, aiul is often done, as long as a sufficient num- 

 ber of characters, let them be ever so unimportant, betrays the 

 hidden bond of community of descent. Let two forms have 

 not a single character in conunon, yet if these extreme forms 

 are connected together by a chain of intermediate groups, we 

 may at once infer their community of descent, and we put 

 them all into the same class. As we find organs of high 

 physiologiortl importance — those which serv'C to preserve life 

 under the most diverse conditions of existence — are generally 

 the most constant, we attach especial value to them ; but if 

 these same organs, in another group or section of a group, are 

 found to differ much, we at once value them less in our classi- 

 fication. We sliall presently see why embryological charac- 

 ters are of such high classiticatpry importance. Geographical 

 distribution may sometimes be brought usefully into play in 

 classing large genera, because all the species of the same 

 genus, inlial)iting any distinct and isolated region, are in all 

 probability descended from the same ]>arents. 



jinalof/lcal Resemhlanccs. — We can understand, on the 

 above views, the very important distinction between real af- 

 finities and analogical or adaptive resemblances. Lamarck 

 first called attention 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 analo- 

 gical. Among insects there are innumerable instances: tlujs 

 Linnicus, misled by external appearances, actually classed an 

 ho;noi)terous 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 turnips. The resemblance of the 

 greyhound and race-horse is hardly more fanciful than the 

 analogies whicli have been drawn by some authors between 

 widely-distinct animals. On my view of characters being of 

 real importance for classification, only in so far as they reveal 

 descent, we can clearlv understand why analogical or adaj^tive 

 characters, although of the utmost importance to the welfare 

 of tlie being, are almost valueless to the systematists. For 

 aniiMiils belonging to two most distinc-t lines of descent may 

 readily have become adapted to similar conditions, and thus 

 have assumed a close external resemblance ; but such resem- 

 blances will not reveal — will rather tend to conceal their 

 blood-rclalionsliip. We can thus also understand the appar- 



