CLASS MAMMALIA 675 



air, which is forced from it, condenses in the cold atmosphere, 

 appearing like a spout of water. Beneath the skin is a thick 

 layer of fat, or " blubber," which retains the body heat. The 

 teeth are numerous, and conical in shape. 



The common dolphin, Delphinus del phis (Fig. 542), is about 

 seven feet in length; it is common in the Mediterranean, along 

 the western coast of Europe, and in the warmer portions of the 

 Atlantic. The sperm-whale, Physeter macrocephahis (Fig. 544), 

 reaches a length of seventy-five feet, and is the largest toothed 

 whale. Its oil, spermaceti, and blubber are sought by whalers. 

 Cephalopods (p. 264) are its principal food. The narwhale, 



Fig. 544. — The sperm whale, Physeter macrocephahis. (From Flower 



and Lydekker.) 



Monodon monoceras, inhabits Arctic seas; one of its upper teeth 

 is a horizontal, twisted tusk about five feet in length. The killer- 

 whale, Orca orca, occurs in all oceans, is about twenty feet in 

 length, and, as its name implies, is a fierce predatory mammal, 

 killing fish, seals, and other whales. 



Order Mystacoceti. — Whalebone Whales. —The single 

 family (BALyENiD^:) of whalebone whales includes the gray 

 whale, Rhacianectes glaucus, of the North Pacific, the rorqual and 

 fin- whales (Baloenoptcra), the hump-backed whale, Megaptera 

 boops, of the Atlantic and Pacific, and the right whales (Balcena). 

 These whales possess teeth only in the embryo ; they are pro- 

 vided in the adult stage with numerous plates of baleen or whale- 

 bone, which are horny and frayed out at the end (Fig. 543). In 

 feeding the whale takes large quantities of water into its 

 mouth, and then forces it out through the sieve-like whalebone, 



