MAMMALS 



209 



Why does a whale need large lungs ? The tail of a whale 



is horizontal instead 

 . of vertical, that it may 

 steer upward rapidly 

 from the depths when 

 * needing to breathe. 

 The teeth of some 

 FIG. 379- -DOLPHIN. whales do not cut the 



gum, but are reabsorbed and are replaced by horny plates 

 of "whalebone," which act as strainers. Give evidence, 

 from the flippers, lungs, and other organs, that the whale 

 is descended from a land mammal (Fig. 397). Compare 

 the whale with a typical land mammal, as the dog, and 

 enumerate the specializations of the whale for living in 

 water. What change took place in the general form of the 

 body ? It is believed that on account of scarcity of food 

 the land ancestors of the whale, hundreds of thousands of 

 years ago, took to living upon fish, etc., and, gradually be- 

 coming swimmers and divers, lost the power of locomotion 

 on land. Order Why ? . 



Elephants are rapidly becoming extinct because of the 

 value of their 

 ivory tusks. 

 Whales also 

 furnish valua- 

 ble products, 

 but they will 

 probably exist 

 much longer. 

 Why? 



The manatees and dugongs (sea cows) are a closely re- 

 lated order living upon water plants, and hence living close 

 to shore and in the mouths of rivers. Order Why ?^ 



FlG. 380. MANATEE, or sea cow ; it lives near the shore 

 and eats seaweed. (Florida to Brazil.) 



