VERTEBRATA. 



349 



FIG. 342. -Greenland Whale (Balcena mysticetwt). North Atlantic. 



otlier Cetaceans teeth are developed, especially in Dol- 

 phins and Porpoises ; bnt the Sperm Whale has them only 

 in the lower jaw, and the Narwhal can show but a single 

 tusk. The Dolphins are the only Mammals having no 

 organ of smell. 



8. Sirenia resemble the Cetaceans in shape, bnt are close- 

 ly allied to the hoofed animals in organization. They 

 have the limbs of the Whales, and are aquatic ; bnt they 

 are herbivorous, and frequent great rivers and estuaries. 

 They have two sets of teeth, the Cetaceans having but 



