90 A BOOK OF WHALES 



in the whale it is precisely the reverse. Hence the 

 same general result is brought about in a totally 

 diverse way in the two orders of aquatic mammals. 



WHALES AND SIRENIA 



The Sirenia form the third most important and the 

 last group of aquatic mammalia. They are a limited 

 race to-day, though there are remains of more 

 abundant genera in the past. Living now are only 

 the two genera, Manatus and Halicore. The former 

 are South American, West Indian, and West African; 

 they are coast-living and fluyiatile animals, which 

 browse along" the bottom of the sea or of rivers 



O 



upon algae. Thus is derived their name of Sea-cows. 

 There seems to be four species of this genus. 

 Halicore, the Dugong, is an eastern creature appar- 

 ently of only one species. 



Most persons are aware that quite recently there 

 lived on the shores of Behring's Straits a third variety 

 of this group of mammals, the Rhytina, or Steller's 

 Sea-cow. This has been extinct since about 1770. 

 But, as its external characters are known, it may come 

 into the following comparison of Sirenia with whales. 



The general form of the body of these sea creatures 

 is not especially whale-like ; they offer, as it were, an 

 intermediate, incomplete form, half-way between the 

 purely terrestrial animal and the totally aquatic whale. 

 Dr. Semon, who observed the Dugong in Torres' 

 Straits, remarks of it that it appears to the eye 

 "more fish-like than seals, and more mammal-like 

 than whales." 



