STRUCTURE AND DEVELOPMENT 37 



characters beneath their minor differences is an indication 

 of their common ancestry. 



Thus at the very outset our simple illustration es- 

 tablishes the most fundamental principle of comparative 

 anatomy. Let us see how it works further. The 

 Manx cat possesses an abbreviated tail, although in 

 other respects it is practically the same as the familiar 

 long-tailed form ; the Angora and the Persian differ 

 in having long hair. All of these animals are so much 

 alike in so many respects, and so closely resemble 

 the wild cats, that it is not unreasonable to regard them 

 all as the descendants of the same original wild ances- 

 tors, and as the varying products of lines which branched 

 out from the same stock in different directions and 

 at different times. It is, in a word, their ''cat-ness" 

 which demonstrates their relationships. But common 

 sense need not stop here. Guided by the facts of ana- 

 tomical similarity, it convinces us that the dun-colored 

 lion and puma, the striped tiger and the spotted leopard 

 are simply cats of a larger growth whose remoter 

 ancestry is one with that of the previously cited forms. 

 Not until we explore and compare their several systems 

 do we see how thoroughgoing is their uniformity in 

 structural plan. And because reason justifies the view 

 regarding the origin of domestic cats from wild ances- 

 tors, the evolution of all the various members of the cat 

 tribe must be acknowledged. These animals exhibit 

 a fundamental likeness, which, to employ a musical 

 analogy, is the "theme" of ''cat-ness," and they are so 

 many variations of this theme. 



The members of another tribe of the familiar car- 

 nivora display in their own way the same kind of evi- 



