TOOTHED WHALES AND THEIR ANCESTRY. 55 



CHAPTEE VI. 



TOOTHED WHALES AND THEIR ANCESTRY. 



WITHIN the entire limits of the great mammalian class, 

 there are, perhaps, no creatures which arouse a larger 

 amount of interest both among the general public and 

 among naturalists than those included under the names 

 of whales, dolphins and porpoises, and collectively known 

 as cetaceans. One reason for this universal interest is, 

 doubtless, that among these denizens of the deep are com- 

 prised the largest animals, not only of the present day, 

 but likewise, so far as our information allows us to speak, 

 of all epochs. Then, again, the fact that such apparently 

 fish-like creatures are really warm-blooded mammals, 

 suckling their young in the manner distinctive of all other 

 members of the class, and being under the necessity of 

 coining to the surface at certain intervals for the purpose 

 of breathing, cannot fail to strike even the most unobser- 

 vant mind as being something quite beyond the ordinary. 

 Moreover, the momentary glimpses which in general are 

 all we obtain of these animals, and the halo of mystery 

 which still to a great extent enshrouds their mode of life, 

 are likewise important elements in generating the wide- 

 spread interest they arouse. To the zoologist, cetaceans 

 are indeed not only of prime importance as being the sole 

 mammals which have assumed a purely fish-like form, and 

 have become so thoroughly adapted to a completely pelagic 

 life as to be unable to exist on land, but their study gives 

 rise to many problems as to their origin and relationships, 

 and the mode in which they attained their present con- 

 dition. 



Into the consideration of the leading external features 

 of cetaceans we need not enter very fully, merely pointing 

 out that while the general contour of the body is fish- 

 like, the tail-fin, or flukes, differs essentially from that 

 of a fish in being horizontal instead of vertical ; while 



