AND COMPARATIVE ANATOMY. 41 



Some live altogether on flesh ; others on vegetable mat- 

 ter ; some eat incessantly, as our common graminivorous 

 quadrupeds; others are satisfied with a full meal once a 

 day, as the beasts of prey ; and others, as certain reptiles, 

 will eat only once in several weeks, and can even support 

 an abstinence of many months. 



To many animals the interruption of respiration for a 

 minute or two is fatal ; some can go without breathing for 

 an hour, for many hours, or for days; and others pass months 

 together without the exercise of this function, in a condition 

 of inactivity and torpor hardly distinguishable from death. 



To many, a slight injury of some organ is fatal; some 

 survive the loss of the most important members, and even 

 reproduce them ; some, when divided into two or more por- 

 tions, have the power of forming an entire individual from 

 each fragment. 



It is the business of the philosophical zoologist to observe 

 closely all the circumstances of these interesting phenomena, 

 and of many other analogous ones ; to trace their con- 

 nexions with the rest of the economy, and with the peculiar 

 organization of each animal ; to compare together all the 

 diversities and modifications; and thus to arrive, if possible, 

 at the rational theory or just explication of their causes. 



The gradations of organization, and the final purposes 

 contemplated by Nature in the construction of her living 

 machines — two interesting and much-agitated subjects in 

 the philosophy of natural history — receive their only clear 

 illustration and incontrovertible evidence from comparative 

 anatomy. Many naturalists have pleased themselves with 

 arranging the animal kingdom in a successive series, accord- 

 ing to external form ; and have fancied it a peculiar mark 

 of wisdom and beauty in the creation, that there are no 

 abrupt changes, no breaks in the arrangement, but the most 

 gradual and gentle transition from link to link throughout 

 the whole chain. These views will not bear the test of im- 

 partial scrutiny, which soon destroys the belief in such a 

 chain of beings, so far as the basis of external figure goes. 

 On the other hand, the pursuits of zootomy, in unfolding the 



