380 



SYSTEMATIC ZOOLOGY. 



from the fact that they bear upon the lower sides of the 



upper jaw hundreds of long 

 parallel plates of so-called 

 whalebone or baleen. These 

 plates are fringed at the end, 

 and the whole apparatus forms 

 an efficient strainer, used in 

 separating the small animals 

 upon which these whales feed 

 from the surrounding water. 



FIG. 167. Section through the head T-t :<, 

 of a whale one whale (after Boas), 



showing ho-v the plates of baleen 



(w) are arranged on either side of 



the mouth-cavity (m). The true mnrnrrm'k 



bones are shown black. 



that tViP 



! 



qrnnno- 

 nomir TViP riVVit 



whales of the Arctic seas 



reach a length of sixty feet, the razor-back whales are 

 still larger, wh:'le the sulphur bottoms and silver bottoms 

 (so called on account of the color of the lower surface) 

 attain a length of from 90 to 95 feet. 



ORDER VII. SIRENIA (Sea-cows). 



These are whale-like animals, with the same flippers and 

 the same horizontal tail, but they differ from the whales in 

 the possession of an evident neck, and of sparse hair or 

 bristles all over the body. Besides these features all, 

 except the extinct Rytina, have flat-crowned molar teeth. 

 The living forms are very few. Rytina, which lived near 

 Bering Strait, was exterminated in the last century. The 

 dugong is the representative of these forms in the Indian 

 Ocean, while the three species of manatees come, one 

 from Africa, the other two from the eastern coasts of 

 America (fig. 168). All the sea-cows are vegetable 

 feeders, living upon seaweed or, in the case of the manatees, 

 upon the plants found in fresh-water streams as well. 



