CLASS MAMMALIA. 205 



coating to withstand the tremendous pressure of water* 

 and to protect the body from the freezing cold.f 



To keep the water out of the lungs when diving, 

 the blow-holes are provided with valves that, like a cork 

 in a bottle, close more firmly the greater the pressure 

 outside. 



ORDER SIRENIA (si re'm a). 



The Manatee (man a te'), or Sea-cow, ranging from 

 Florida to the Amazons, has the body partially covered 

 with hair, the hind limbs absent, and the fore limbs 

 flipper-like, with small nails. The nostrils, provided with 



FIG. 354. 



Trick' e chus mnn' a tus. Manatee. (^.) 



valves, are placed on the end of a large and fleshy snout, 

 and the neck is shortened, there being only six cervical 

 vertebrae. It frequents estuaries and large rivers, wher- 

 ever it finds growing the aquatic plants upon which it 

 feeds, hence named an "herbivorous whale." Three spe- 

 cies are recognized. Allied to the Manatee is the Du- 

 gong, of Australia and India, and a genus living on the 

 coast of Kamtchatka in the last century, but now extinct. 



* The whale often descends to the depth of a mile, where, according to 

 Scoresby, the pressure upon it is equal to 200,000 tons, and wood becomes so 

 water-soaked as not to rise again. When, on being struck, the whale sinks to 

 such a depth, the veins being unprovided with valves, the blood leaves the body 

 through the wound in a continual hemorrhage, death soon resulting. 



t This enormous bulk of fat is lighter than the water, and gives great buoy- 

 ancy, so that the dead body of a whale floats until the layer of blubber is 

 "flensed off," when it sinks. 



