1883.J on WImUs, Pad and Present, oM their ProhaJAe Origin. 361 



and middle-sized Cetacea, and though sucli smaller species as the 

 dolphins and porpoLses are not usually spoken of ag whales, they may 

 for all intents and purposes of zoological science be included in the 

 term, and will come within the range of the present subject. Taken 

 all together the Cetacea constitute a perfectly distinct and natural 

 order of mammals, characterised by their jjurely aquatic mode of life 

 and external fishlike form. The body is fusiform, passing anteriorly 

 into the head without any distinct constriction or neck, and posteriorly 

 tapering off gradually towards the extremity of the tail, which is pro- 

 vided with a pair of lateral p»ointed expansions of skin supported by 

 den-se fibrous tissue, called "' flukes,'' forming together a horizontally- 

 placed, triangular propelling organ. The fore-limbs are reduced to 

 the condition of flattened ovoid paddles, incased in a continuous in- 

 tegument, showing no external sign of division into arm, forearm, and 

 hand, or of separate digits, and without any trace of nails. There are 

 no vestiges of hind-limbs visible externally. The general surface of 

 the body is smooth and glistening, and devoid of hair. In nearly all 

 species a compressed median dorsal fin is present. The nostrils open 

 separately or by a single crescentic valvular aperture, not at the 

 extremitv of the snout, but near the vertex. 



ATn'TnaU of the order Cetacea aboxmd in all known seas, smd some 

 species are inhabitants of the larger rivers of South America and 

 Asia. Their organisation necessitates their life being passe^l entirely 

 in the water, as on the land they are absolutely helpless ; but they 

 have to rise very frequently to the surface for the purpose of respira- 

 tion. They are all predaceous, subsisting on living animal food of 

 some kind. One genus alone (Orca) eats other warm-blooded animals, 

 as seals and even members of its own order, both large and small. 

 Some feed on fish, others on small floating Crustacea, pteropods, and 

 medussD, while the staple food of many is constituted of the various 

 species of Cephalopods, chiefly Loligo and other Teuihddae, which 

 must abound in some seas in vast numbers, as they form almost the 

 entire support of some of the largest members of the order. With 

 some exceptions the Cetacea generally are timid, inoffensive animals, 

 active in their movements, sociable and gregarious in their habits. 



Among the existing members of the order there are two very dis- 

 tinct types — the Toothe«i TVhales, or Odantoceti, and the Baleen 

 Whales, or ^lystacoceti, which present throughout their organisation 

 most markedly distinct structural characters, and have in the existing 

 state of nature no transitional forms. The eirtinct Zeuglodon, so far 

 as its characters are known, does not fall into either of these groups as 

 now constituted, but is in some respects intermediatej and in others 

 more resembles the generalise! mammalian type. 



The important and inter _ problem of the origin of the 



Cetacea and their relations to : : zls of life is at present involved 

 in the greatest obscurity. They present no more signs of affinity 

 with any of the lower classes of vertebrated animals than do many of 

 the members of their own class. Indeed, in all that essentially dis- 



