236 VERTEBRATA. MAMMALIA. 



small, and the whalebone short. It is common in 

 the Arctic seas, and occasionally descends to our own 

 shores.* 



Thus we finish the first portion of the great chain 

 of animated being : that most important, most inter- 

 esting, and most highly endowed class of animals, 

 which bring forth and suckle living young. While 

 we have observed a vast variety of powers, instincts, 

 and habits ; of motion, food, and locality ; we have 

 become acquainted with the remarkable fact, that 

 this variety is supplied, not by the creation of a new 

 set of organs for every change, but by a modification 

 of existing ones, few and simple in themselves, which 

 seem to have been formed as a model from which 

 there has been no deviation. Slight alterations in 

 form, size, or situation, often produce a total change 

 in use and power ; and even where the alteration is 

 at its highest, the organs are found to be essentially 

 the same in structure, and easily recognized. And 

 though we are about to witness still wider departures 

 from accustomed forms, we shall find this great law 

 still prevailing, that all the creative designs of God 

 are fulfilled with the least possible expenditure of 

 creative energy, the least possible waste of power. 



* A specimen has been taken in the Thames during the progress of 

 this work. 



