DOLPHINS AND S1EENS. 51 



to the river-bank, raising itself by means of the flippers, 

 and resting with the head and upper part of the body 

 on the shore, while the rest is in the water. 



Having somewhat of the whale tribe in their 

 general form, they have little of the whale's habits. In 

 the first place, they are vegetable feeders, living almost 

 entirely on sea-weed and such like vegetation. Conse- 

 quently, they are obliged to remain close to the land, 

 whereas the whales are uneasy unless they are at some 

 distance from it. 



The structure of the teeth is also different, as they 

 are intended for the mastication of vegetable food, and 

 not for the capture of living animals. There is a dis- 

 tinction between the character of the teeth, the animals 

 having incisors in both jaws, one molar in the upper 

 side of the upper jaw, but no canines ; whereas in the 

 porpoise and dolphin, all the teeth look like canines, 

 and, indeed, are used for the same purpose namely, 

 securing the prey. 



Respiration and circulation are in the Sirens diffe- 

 rent from the same functions in the whales. Living in 

 comparatively shallow waters, and feeding upon a 

 vegetation that never grows at any great depth, the 

 animal does not require to possess the power of 

 remaining under water for any lengthened period. 



Consequently, it does not possess the great sub- 

 sidiary mass of blood-vessels which play so important 

 a part in the economy of the whale, and the nostrils 

 are placed at the end of the muzzle, like those of most 

 mammals. The peculiar " blowing " of the whale tribe 

 is not found in the Sirens, as they are not obliged to 

 aerate the vast supply of blood which is needful in 



