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THE CETACEANS 



Form 



The assumption of a fish-like form by the Cetaceans is one of the 

 best-marked examples of what are known as adaptive characteristics, 

 which are merely produced in order to suit the animals in which they exist to their 

 external surroundings, and have no sort of connection with their affinities. The 

 fish-like resemblances of the Cetaceans are, moreover, not so close as they may 

 at first sight appear; since the tail fin, instead of being vertical, is horizontal, while 

 the structure of the skeleton of the fore-limb is totally different from that of 

 any fish. The general fish-like form of the body is, however, that best adapted for 

 progression through the water, which affords sufficient reason for its having been 

 acquired in the present group of animals; and we may likewise mention that 

 Cetaceans generally resemble fish in having the upper part of the body colored dark, 

 while the under parts are light, such a coloration rendering the animals in which 

 it occurs not easily seen, either from above or below, when in their native element. 



That whales are not even directly descended from fishes is evident 

 No Connection r ,, r r ,, . , ,, . , . . , .. , 



from the tact or their breathing atmospheric air, by means of lungs, 



for if they had so originated it would be quite clear that they would 

 have retained fish-like gills, and thus have avoided the necessity of coming 



SKELETON OF GREENLAND WHALE. 



periodically to the surface for the purpose of breathing. It is probably for this 

 reason that Cetaceans have their tails with the expansion placed in a horizontal 

 instead of a vertical plane, since the strokes of such a horizontally -expanded organ 

 are the best calculated to bring an animal rapidly to the surface. 



The additional circumstance that Cetaceans retain traces of the 

 hairy covering, which is so characteristic of Mammals in general, 

 affords evidence that they derive their origin from terrestrial Mammals; and, taken 

 together with the absence of hind-limbs, is amply sufficient to disprove any notion 

 that they themselves are in any sort of way connected with the ancestral stock from 

 which the other members of the class have originated. Cetaceans may, therefore, 

 be regarded as some of the most specialized of all Mammals. With regard to the 

 terrestrial Mammals to which these animals are most closely related, there is still 

 great uncertainty and some difference of opinion among zoologists. Sir W. H. 

 Flower is inclined to consider that they show more resemblances to Ungulates, and 

 especially the Even-Toed group; but the teeth of the earliest forms are quite unlike 



