HISTORY OF ZOOLOGY. 



49 



single great inductive proof in favor of the Theory of 

 Descent. 



cA c 



FIG. io. Tail-fins of various fishes. (From Zittel.) ch, chorda, a, 6, c; cover-plates. C, 

 D, Homocercal fins, C, of Amiacaira ; D, of Trutta salar. (By a still greater upward 

 bending of the notochord and vertebral column the dorsal portion has almost entirely 

 disappeared and the ventral portion almost alone forms the fin, externally apparently 

 symmetrical, but in its internal structure very asymmetrical.) 



Study of the Distribution of Animals. Finally 

 now in regard to Animal Geography : here we learn that 

 the present state of distribution of animals is the product 

 of past hundreds and thousands of years. It will therefore 

 be possible from this to figure out many of the earlier con- 

 ditions of things, if one proceeds with the utmost caution 

 and after overcoming extreme difficulties. 



If we assume that from the beginning all animal species 

 were constituted as they now are, they would then have 

 been placed by the purposeful Creator in the territories 

 best suited to their organization ; their distribution would 



