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THE POPULAR SCIENCE MONTHLY. 



ually toward the extremity of the tail, which is provided with a pair 

 of lateral pointed expansions of skin supported by dense fibrous tissue, 

 called "flukes," forming together a horizontally placed, triangular pro- 

 pelling organ. The fore-limbs are reduced to the condition of flattened 

 ovoid paddles, incased in a continuous integument, showing no external 

 sign of division into arm, fore-arm, 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 extremity of the snout, but near the 

 vertex. 



Animals of the order Cetacea abound in all known seas, and some 

 species are inhabitants of the larger rivers of South America and Asia. 



Their organization necessi- 

 H^ tates their life being passed 

 entirely in the water, as on 

 g the land they are absolutely 

 jg helpless ; but they have to 

 rise very frequently to the 

 surface for the purpose of 

 respiration. They are all pre- 

 daceous, 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 medusa?, while the staple food of 

 many is constituted of the various species of Cephalopods. 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 toothed whales, or Odontoceti, and the baleen (whale- 

 bone) whales, or Mystacoceti, which present throughout their organi- 

 zation most markedly distinct structural characters, and have in the 

 existing state of nature no transitional forms. 



The problem of the origin of the Cetacea and their relations to 

 other forms 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 distinguishes a mammal from 

 one of the oviparous vertebrates, they are as truly mammalian as 

 any, even the highest, members of the class. Any supposed signs 

 of inferiority are simply modifications in adaptation to their peculiar 

 mode of life. In the present state of our knowledge, the Cetacea 



Fig. 1. Common Dolphin. 



