VERTEBRATA: MAMMALIA. 689 



are a good deal smaller than the males. The head is disproportion- 

 ately large, as in the Balcenida, forming more than one-third of the entire 

 length of the body. The snout forms a broad truncated muzzle, and the 

 nostrils are placed near the front margin of this. The Sperm Whales 

 live together in troops or "schools," and they are found in various seas, 

 especially within the tropics. They are largely sought after, chiefly for 

 the substance known as "spermaceti ;" but besides this they yield oil and 

 the singular body called "ambergris." The spermaceti is a fatty sub- 

 stance, which has the power of concreting when exposed to the air, being 

 in life a clear white oily liquid. It is not only diffused through the entire 

 blubber, but is also contained in special cavities of the head. The sperm- 

 oil yielded by the blubber is exceedingly pure, and is free from the un- 

 pleasant odour of ordinary whale-oil. The ambergris is a peculiar sub- 

 stance which is found in masses in the intestine, and is probably of the 

 nature of a biliary calculus, since it is said to be composed of a substance 

 very nearly allied to cholesterine. It is used both as a perfume itself, and 

 to mix with other perfumes. 



Fam. 3. Delphinidce. This family includes the Dolphins, 

 Porpoises, and Narwhal, and is characterised by usually pos- 



Fig- 385. Side-view of the skull of Delphinus tursio. (After Cuvier.) 



sessing teeth in both jaws : the teeth being numerous, and 

 conical in shape (fig. 385). The nostrils, as in the last fam- 

 ily, are united, but they are placed further back, upon the top 

 of the head. The single blow-hole or nostril is transverse and 

 mostly crescentic or lunate in shape. The head is by no means 

 so disproportionately large as in the former families, usually 

 forming about one-seventh of the entire length of the body. 



The most noticeable members of this family are the true 

 Dolphins, the Porpoises, and the Narwhal. 



The Dolphins have an elongated snout, separated from the 

 head by a transverse depression. The common Dolphin (Del- 

 phinus delphis, fig. 386) is the best-known species. It aver- 

 ages from six to eight feet in length, and has the habit of 

 swimming in flocks, often accompanying ships for many miles. 

 The female, like most of the Cetacea, is uniparous. The 

 Dolphin occurs commonly in all European seas, and is espe- 

 cially abundant in the Mediterranean. 



The common Porpoise {Phoccena communis} is the commonest and 

 smallest of all the Cetacea, rarely exceeding four feet in length. The head 



2 X 



