£98 ON THE CLASSES OF THE 



at some period or other of their lives a greater or less ten- 

 dency to shed their external covering, and thus to deve- 

 lope a new form ; and that there is some reason therefore 

 for arguing, that where this tendency to metamorphosis is 

 most revealed, there the type of perfection at which the 

 whole group aims is the nearest attained. Hexapod in- 

 sects possess the means of living in the water and on its 

 surface, in the air and on the earth, often combining all 

 these powers in one individual ; and with respect to the 

 functions of nutrition and generation, they appear to be 

 quite as perfectly organized as animals which are usually 

 conceived to be superior to them in the scale of being. 

 Yet these functions must not be considered as executed 

 by similar organs or by the same process in the Annulose 

 and Vertebrated animals. There exists a wide distinc- 

 tion between them, so wide indeed that notwithstand- 

 ing their activity, industry, and ingenuity, insects have 

 in the later systems founded on comparative anatomy 

 been placed beneath the Mollusca, only because these last 

 possess nearly the same apparatus of organs for digestion, 

 circulation and respiration as the Vertebrated animals. 

 Two exceptions however to this proceeding are so honour- 

 ably conspicuous as to deserve mention ; I allude to the 

 ingenious authors of the article Classification in Rees's 

 Cyclopedia, and of the article Nerfs in the Dictionnaire 

 d'Histoire Naturelle. 



It may in fine be observed, that in proportion to the 

 perfection of the structure of the animal, life becomes 

 more concentrated, more confined to a particular part ; and 

 various parts, when maimed or amputated, become less 

 capable of being reproduced. The Polype may be di- 

 vided into as many distinct animals as there are divisions. 



