xiv WHALES NOT FISHES 187 



in which the whale differs from the fish, it agrees with ordinary mammals. 

 Therefore the zoologists put the whales into the same class with the mam- 

 mals, and not into that of the fishes. But this conclusion implies the 

 assumption that animals should be arranged according to the totality of 

 their resemblances. It means that the likenesses in structure of whales 

 and mammals are greatly more numerous and more close than the like- 

 nesses between whales and fishes. 



It also means, if the derivative hypothesis of animal species is 

 true, that the whale is far more nearly related to, say, a horse 

 or a cow than it is to a cod or a shark. 



It is decided, then, that, from the point of view of a 

 zoologist at all events (whatever the fisherman and the man 

 of business may continue to say), the whales and their allies 

 belong to the class Mammalia, and not to that of Pisces. We 

 can easily fix their place in that class as constituting a distinct 

 and clearly defined order, the Cetacea, derived from the Latin 

 word cetus = a whale. Although the term " whale " is 

 generally, if somewhat vaguely, restricted to the larger and 

 middle-sized members of the order, the smaller ones, commonly 

 called " dolphins " and " porpoises," to all intents and purposes 

 belong to it, and no line can be drawn to separate them except 

 size ; and even in this respect there is a regular gradation 

 between the colossal rorqual of 80 feet in length to the 

 pontoporia, or dolphin of the estuary of the La Plata, which 

 scarcely exceeds a yard from snout to tail. On this occasion, 

 after a few general ( observations on the group, I propose to 

 limit myself almost entirely to the larger species, to which 

 the term " whale " is most especially appropriate, and which 

 have the greatest interest to man, on account of the industries 

 to which the commercial value of their products gives rise. 



Taken altogether, as I have mentioned, the Cetacea 

 constitute a perfectly distinct and natural order of mam- 

 mals, characterised by their purely aquatic mode of life 

 and external fish-like form. Their body passes anteriorly 

 into the head without any distinct constriction or neck, and 

 posteriorly tapers off gradually to 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 propelling organ, quite different 



