CETACEA. 553 



Order 5. CETACEA.* 



Aquatic, fish-like, naked forms without hind limbs. The head 

 passes continuously into the body and the nasal apertures are on 

 the top of the head. 



The Cetacea are entirely aquatic animals. Though fish-like 

 in appearance, they are mammalian in structure, but they stand 

 far apart from other mammals, and it is impossible to guess at 

 their origin. Some species attain a colossal size, and are among 

 the largest, if not the largest, of all known animals, whether living 

 or extinct. The cervical region of the vertebral column is 

 extremely short, and there is apparently no neck, the head 

 passing directly into the trunk. There is a horizontally-ex- 

 panded caudal fin (the lateral expansions of which are called 

 flukes), and often a fatty dorsal fin. Hairs are almost entirely 

 absent, being represented only by a few bristles on the upper 

 lip, which are present during the whole of life or only during 

 the foetal period, and are without sebaceous glands. On the 

 other hand there is developed beneath the thick skin in the 

 subdermal cellular tissue a considerable layer of fat (blubber), 

 which to a certain extent takes the place of fur and serves both 

 to prevent the loss of heat and to diminish the specific gravity. 

 It does not, however, necessaiuly follow that the absence of hair 

 is caused by the presence of blubber, for in the seals both hair 

 and blubber are present. The absence of hair is a jDroperty 

 of the whale, and cannot be accounted for. The same remark 

 applies to the scanty hair}^ covering found in some other 

 mammals. The head is large, and the opening of the 

 external ear is ver}^ minute and vv ithout a pianna. The eyes are 



* Hunter, Observations on the structure tmd oeconoray of whales. 

 Phil. Trans., 1787. F. Cuvier, Hi»toire naturellc des Cetaces, Paris, 1836. 

 .D. F. Eschricht. Unters. uher die. nordisnhen Walthiere, Leipzig, 1849. 

 D. F. Escliricht og J. Reinhardt, Om Nordhvalen, Copenhagen, 1861. 

 van Beneden and Gervais, Osteogrnphie des Cetaces viv. et foss., 1 868-1880, 

 1 vol. and atlas 64 plates, van Beneden, Histoire Nat. des Cetaces des 

 iners d' Europe, 1 vol. Svo, 1880. C. M. Scammon, Marine Animals oj 

 the N.W. coast of N. America, 1874. J. F. Brandt, Unters. ilb. die foss- 

 u. subfoss. Cetaceen Europa's, Mem. Acad. Petersbourg, (7), 20, and 21, 

 1873-4. W. H. Flower, On the characters and divisions of the families 

 of the Delphinidae. Proc. Zool. Soc, 1883, p. 466. F. W. True, Review 

 of the Family Delphinidae, Bull. U. S. Nat. Mus., 1889. R. Lydekker, 

 Cetacea of the Suffolk Crag, Quart. Journ. Geol. Soc, 42, 1887, p. 7, and 

 Catalogue of the fossil mammalia in the British Museum, 1887. F. E, 

 Beddard, A Book of Whales, London, 1900. 



