16f ZOOLOGY. 



proper for the support of their future progeny, is almost in- 

 credible, some kinds ascend rivers many miles in extent, and 

 in defiance of all obstacles, such as rapid falls, &c., will sur- 

 mount these, by leaping, or throwing themselves out of the 

 water, frequently many feet high. 



Numerous species retire within the Arctic circle on the 

 approach of winter, where, owisg to the rigour of the season, 

 their young are less liable to be destroyed by predaceous 

 animals, still here they are not exempt from their attacks, 

 for though miriads of wild fowl quit these inhospitable climes 

 at the Autumnal season, and seek milder climates, yet amidst 

 this region of Ice and Snow, they have their natural enemies 

 to contend with, and guard against : the Polar Bear pursues 

 them even under the ice, and not unfrequently perishes in 

 the pursuit, as in such situations, being unable to take fresh 

 inspiration of air, it soon drowns ; the Walrus, the Manati, 

 the various species of Seals, the endless variety of Gulls, 

 Cormorants, Shags, Penguins, and other piscivorous Birds, 

 are at constant war with, and derive nearly their whole sup- 

 port from this class : add to which, that it is common to 

 many (perhaps most) species, to devour not only others, 

 but also individuals of their own kinds ; the vast encrease of 

 this useful class, isnever found to encroach or extend beyond 

 its prescribed limits, so as to inconvenience or intrude upon 

 the other classes. 



While the greater number make their brumal retreat to 

 the north, there are others, which not finding their wonted 

 food there, during the winter, repair to the south, and thus 



