Classification. 39 



adaptive, and resemblances as homological or of 

 meaning in reference to a natural classification. To 

 take another and more detailed instance, the Tas- 

 manian wolf is an animal separated from true wolves 

 in a natural system of classification. Yet its jaws and 

 teeth bear a strong general resemblance to those of 

 all the dog tribe, although there are differences of 

 anatomical detail. In particular, while the dogs all 

 have on each side of the upper jaw four pre-molars 

 and two molars, the Tasmanian wolf has three pre- 

 molars and four molars. Now there is no reason, so 

 far as their common function of dealing with flesh is 

 concerned, why the teeth of the Tasmanian wolf 

 should not have resembled homologically as well as 

 analogically the teeth of a true wolf; and therefore 

 we cannot assign any intelligible reason why, if all the 

 species of the dog genus were separately created with 

 one pattern of teeth, the unallied Tasmanian wolf 

 should have been furnished with what is practically 

 the same pattern from a functional point of view, 

 while differing from a structural point of view. But, 

 of course, on the theory of descent with modifica- 

 tion, we can well understand why similarities of 

 habit should have led to similarities of structural 

 ' appearance of an adaptive kind in different lines of 

 descent, without there being any trace of such real or 

 anatomical similarities as could possibly point to 

 genetic relationship. 



Lastly, to adduce the only remaining argument 

 from classification which I regard as of any consider- 

 able weight, naturalists have found it necessary, while 

 constructing their natural classifications, to set great 

 store on what Mr. Darwin calls " chains of affinities." 



