WHALES AND SIREN1A 93 



a fin-like form. But there are differences in the 

 completeness with which this metamorphosis has 

 progressed. The Dugong has become more com- 

 pletely aquatic in this particular than the Manatee. 

 The latter, with the exception of the species M. 

 inunguis, has preserved the nails upon the extremities 

 of the fingers, while these have entirely disappeared 

 in the Dugong. Moreover, in the latter genus the 

 forearm no longer takes any part in the formation 

 of this "fin" a feature which, of course, is shared 

 by the Cetacea. Professor Kiikenthal has, however, 

 called attention to a curious similarity which exists 

 between the hand of these Sirenians to that of the 

 sea-lions, in the shape of numerous papillae and 

 grooves upon the under surface. This is associated 

 in the Otariidae with a partial life upon land, and 

 the existence of these structures in the Sirenia seems 

 to indicate a more recent abandonment of the terres- 

 trial life than has been the case with the Cetacea, 

 whose flippers are smooth. A reason for their re- 

 tention, however, in the Dugongs is perhaps to be 

 found in the fact that these creatures graze upon beds 

 of seaweed as a Herbivorous mammal does upon a 

 field of grass ; and the rough papillae prevent the 

 animal from slipping when thus engaged in cropping 

 its food. In the skeleton of the fore limb there are 

 no strong resemblances to the whales, for the 

 joints between the bones are well developed, and 

 there are only slight beginnings of hyperphalangy, 

 so characteristic a feature of the Cetacea. 



When we turn to the internal structure of the 



