.VERTEBRATA. 



349 



Fig. 342.— Greenland Whale (Balcena mysticetus). North Atlantic. 



other Cetaceans teeth are developed, especially in Dol- 

 phins and Porpoises ; but 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, but are close- 

 ly allied to the hoofed animals in organisation. They 

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

 are herbivorous, and frequent great rivers and estuaries. 

 They have two sets of teeth, the Cetaceans having but 



