MARINE MAMMALS, AND FISHES 97 



slippery, and fleeting prey. The fresh-water pike, 

 whose more sluggish habit of rushing out from 

 his den, under the alder roots, on passing trout, 

 renders speed less essential, has still a similar 

 arrangement of teeth. 



The shape, together with the structure of the 

 skeleton, admit of more than one bend in the body 

 at a time. Thus the creature passes through the 

 water with a rippling motion ; which, albeit graceful 

 as that of the snake, has something of the same 

 sinister meaning. 



The marine forms belong to the sharks, and dog- 

 fishes. The transverse, or crescentic mouth under 

 the prominent snout, seems to mark them out as 

 bottom feeders, .and necessitates the turning over 

 in an awkward manner, when any object on the 

 surface has to be grasped. It is quite possible that 

 the disagreeable propensities, which make some of 

 the species the terror of the tropical seas, and have 

 come to be associated in the popular mind with 

 the whole, was an afterthought, a habit painfully 

 acquired, and still clumsily executed. 



An interesting feature, not common among fishes, 



is that, in a majority of cases, the young are brought 



forth alive. The exceptions are the true dog-fishes, 



which are small round sharks ; and the skates or 



7 



