64 ANIMAL LIFE PAST AND PRESENT. 



strokes of the powerful flukes being admirably suited 

 to effect this object with the greatest speed. Then, 

 again, the number and structure of the paddles and 

 fins are quite different from those obtaining in fishes. 

 Thus, a Whale (using this term for the whole group of 

 allied animals) has only a single pair of flippers (Fig. 

 14), which correspond to the fore limbs of ordinary 

 Mammals, and to the pectoral fins of fishes. These, 

 however, although presenting certain peculiarities, are 

 evidently only modifications of the normal mammalian 

 fore limb, and are devoid of any structures correspond- 

 ing to the fin-rays of fishes. They have lost all out- 

 ward trace of the digits, being completely invested in 

 a common integument. Then, again, the pelvic fins of 

 fishes are wanting ; the only traces of hind limbs being 

 certain rudimentary bones found deeply bedded in the 

 flesh of some of the species, which represent the 

 aborted hind legs of quadrupedal Mammals. If, more- 

 over, Whales have any unpaired fins the single one is 

 situate on the back (Fig. 14), and its structure is quite 

 different from that of the dorsal fin of a fish. In order 

 to enable them to stay for long periods below the 

 surface, the circulatory system of Whales develops a 

 number of net-like arrangements of the vessels in 

 which a supply of fresh blood is stored up. 



It would involve too much detail to enter into the 

 consideration of the numerous other resemblances 

 existing between Whales and "ordinary Mammals, but 

 there can be no sort of doubt but that they are members 

 of the class ; and likewise practically none that they 



