PROGRESSION ON AND IN THE WATER. 



73 



in the pipefish, whose motions are unwontedly shiggish. 

 The twisting of the tail is occasionally well marked in the 

 swimming of the salamander. In those remarkable mammals, 

 the whale,^ porpoise, manatee, and dugong (figs. 33, 34, and 

 35), the movements are strictly analogous to those of the fish, 



Fig. 31, — The Manatee [Manatus Americamis). In fhis the anterior extremities 

 are more developed than in the porpoise, but still the tail is the great organ 

 of natation. Compare with fig. 33, p. 73, and with fig. 30, p. 65. The shape 

 of the manatee and porpoise is essentially that of the fish. — Original. 



the only difference being that the tail acts from above down- 

 wards or vertically, instead of from side to side or laterally. 

 The anterior extremities, which in those animals are com- 

 paratively perfect, are rotated on their long axes, and applied 

 obliquely and non-obliquely to the water, to assist in balanc- 

 ing and turning. Natation is performed almost exclusively by 

 the tail and lower half of the trunk, the tail of the whale 

 exerting prodigious power. 



It is otherwise with the Rays, where the hands are princi- 



i Vide " Remarks on the Swimming of the Cetaceans," by Dr. Murie, 

 Proc. Zool. Soc, 1865, pp. 209, 210. 



