ORGANIC ADAPTATION 



323 



Gophers, and especially the Moles, which are adapted to a subter- 

 ranean existence by bodily modifications which facilitate digging. 



Fig. 204. — A Sloth, Choloepus, walking suspended from a branch. 



(From Allen.) 



Furthermore, the gap between terrestrial and aquatic Mammals is 

 bridged by the Muskrats, Beavers, Otters, and Seals which are 

 more or less equally at home on land and in the water. (Fig. 205.) 



Fig. 205. — Skeleton of a Mole, Talpa europaea. (From Pander and D'Alton.) 



The truly aquatic Mammals, such as the Porpoises and Whales, 

 have completely abandoned the land of their ancestors of the 

 geological past and to-day approach, in adaptations to a marine 



Fig. 206. — Skeleton of a Porpoise. The vestigial pelvic bones are shown 

 imbedded in the flesh. (From Pander and D'Alton.) 



life, the general contour of the primitively adapted aquatic Ver- 

 tebrates, the Fishes. (Fig. 90, 91, 206.) 



Thus the various lines of adaptive radiation of the Mammals from 

 a generalized terrestrial type, such as Gymnura, have provided 



