ZOOLOGY. — ECONOMY 0¥ VERMES. 547 



power of motion to enable them to retire into a more 

 southern region. Now, such an event is provided a- 

 gainst, by the constant prevalence of a current setting 

 towards the south-west, which carries away the ice 

 into a parallel where it can be dissolved, and occa- 

 sions a circulation of water into the frozen regions, 

 from SI warmer climate. And this circulation of 

 the water is beautifully accomplished: for, while 

 the superficial current is performing its office, in 

 carrying away a portion of ice, an under-current 

 setting to the northward, is acting an equally im- 

 portant part, in affording warmth to the seas of the 

 higher latitudes, and preventing the too great accu- 

 mulation of the ice. But how is it, it might be 

 asked, when a current in the waters, inhabited by 

 the minor medusae, is constantly setting to the 

 southward, that these animals are not carried away 

 into a southern region altogether ? This question, 

 if we may be allowed to argue hypothetically, ad- 

 mits of an easy solution. Animals, we find, when 

 possessing any power of moving, though they be of 

 the most imperfect kind of organization, generally 

 employ that power by a sort of instinctive faculty, 

 as may best serve the purposes for which they were 

 called into existence. Now, it would be no stretch 

 of commonly received principles, to suppose, that 

 whenever the minor medusse, &c. are carried to a 

 certain extent southward, they may sink in the 

 water, as far as the stream of the under-currentj 



