452 ZOOLOGY 



burrow twenty yards in a day. For brief periods and in reason- 

 ably firm soil they have been seen to dig a yard in ten minutes. 



Order 3. Sirenia. A small group of aquatic Placentalia, 

 more or less whale-like in form. They are sluggish, ungainly, 

 vegetable feeders. They have no posterior appendages and the 

 anterior are flipper-like, though capable of bending at the elbow. 

 They live near the shore and are represented by two living genera, 

 the sea-cow of our own eastern shores (Manatee), and the 

 Dugong of the Indian Ocean. 



Order 4. Cetacea (Whales, Porpoises, Etc.). The Cetacea are 

 aquatic mammals with a fish-like body. There are no posterior 

 appendages, and the anterior act as paddles, being without joint. 

 The tail is horizontally expanded into a powerful paddle, and a 

 dorsal fin is usually present. Teeth are present in the embryo, 

 but may be lost or replaced by "whale-bone" in the adult. 

 The stomach is chambered. The two mammae are posterior. 

 Hair is very scant, but the layer of fat or "blubber" beneath 

 the skin is very thick, and serves as a non-conductor of heat. 



The whales are the largest living animals. The largest of 

 these, the Greenland whale, may attain a length of seventy-five 

 feet or more. It must be remembered that the whales are air- 

 breathers, and therefore must come to the surface to breathe 

 or "blow." The Cetacea prey on the smaller swimming or 

 floating animals found in the ocean, as fish, squid, Crustacea, 

 etc. Whales are principally sought for their fat and baleen, 

 or whale-bone. 



There are two principal suborders: the toothed whales, and 

 the whale-bone whales. The former include the dolphins, por- 

 poises, grampuses, narwhales, sperm whales, and beaked whales. 

 The right whales, the hump-backed whale, the gray whale, the 

 finback whale, and the sulphur bottom whale lose their embry- 

 onic teeth and produce whalebone. Food is taken with the 

 mouth open and the water is forced out through the whale-bone, 

 eaving the "catch" in the mouth. The sulphur bottom may 

 reach a length of ninety-five feet and a weight of 150 tons. 



Order 5. Ungulata (hoofed animals). This order includes a 

 great number of animals, chiefly herbivorous, that walk on their 

 toes. In these forms the horny growth which we have so fre- 



