THE GENERAL SHAPES OF ANIMALS. 



187 



its axis, and also into other not very dissimilar halves by a 

 plane cutting it transversely. If, as shown in Figs. 275 

 and 276, analogous sections be made of a superior Reptile, the 

 divided parts differ more decidedly. When a Mammal and a 

 Bird are treated in the same way, as shown in Figs. 277, 

 278, and Figs. 279, 280, the parts marked off by the divid 



ing planes are unlike in far greater degrees. On considering 

 the mechanical converse between organisms of these several 

 types and their environments on remembering that the 

 fish habitually moves through a homogeneous medium of 

 nearly the same specific gravity as itself, that the terrestrial 

 reptile either crawls on the surface or raises itself very in 

 completely above it, that the more active mammal, having 



