188 



ZOOLOGY. 



354 Natural Affinities and Analogies of Structure. 

 This tendency of nature to observe one general plan in the 

 construction of her works, leads to another sort of relation - 

 ship which naturalists have called natural affinities. These 

 affinities are always the stronger that they bear on organs of 

 secondary physiological importance, and necessitate less change 



Fig. 130 a. The Human Vertebra the Type of all Skeletons. 



in the general plan of the organiza- 

 tion. Thus it is obvious that the 

 lion, cat, and tiger have strong natu- 

 ral affinities ; between the lion and 

 the dog there still exist natural affi- 

 nities, though obviously less marked; 

 but between the lion and the shark 

 they are extremely feeble, except ing 

 in so far as they both belong to the 

 vertebrata ; finally, between a fish 



\t and an oyster there are none, inas- 



j F* much as these two beings are formed 



n on plans essentially distinct. 



355. Between matured affinity 

 and analogy there is this essential 

 distinction, affiiiilifs are based 

 on the identity, more or less com- 

 plete, of the type: tnnilntiicfs, On R 



resemblance in the details. Thus 

 the bat (Fig. 91), a mammal. 

 pterodactyle, a reptile, and the 

 dactyloptera (89), a fish, have no zoological affinity, pro- 

 perly so called, excepting that they are vertebrate animals; 



Ki 



;. 130 b. The Ideal 



>ra, as viewed by Spix-Oken 

 and St. Hilaire as the Type 

 of all Structures. 



