ANIMAL KINGDOM. 295 



this moreover have excited much surprise, if we have 

 called to mind how much the nature of the respiratory 

 functions must depend on the medium inhabited by the 

 animal. Among the Vertebrata, indeed, circulation and 

 respiration appear to afford the firmest foundation for na- 

 tural distribution ; but the great principle of creation being 

 to combine variety in the means with uniformity in the 

 effect, we find that in the Mollusca, on the other hand, the 

 circulation of the blood varies in its manner ad infinitum, 

 and has accordingly led to one of the most artificial arrange- 

 ments which is known. And yet there are no animals in ex- 

 istence which have the organs connected with the circula- 

 tion more complicated than some of the Cephalopoda. In 

 the Annulose animals also, which correspond with one 

 another so remarkably in the nature of their nervous sy- 

 stem, we find that of circulation to vary from a singularly 

 perfect one till it altogether disappears. An entirely new 

 method of respiration and of nutrition of the parts appa- 

 rently takes place, a method indeed so totally distinct from 

 any which we have yet observed in the Mollusca and Verte- 

 brata, that the most fanciful imagination can never consider 

 them to be modifications of the same. As then these animals 

 are generally constructed on different plans, may we not be 

 permitted, nay is it not absolutely necessary, to suppose 

 that this new and entirely different system of respiration 

 is that which more peculiarly belongs to the group, or in 

 other words is that to which the structure of the animals 

 forming the group tends ? What makes this supposition 

 still more probable is, that the Jnnelides, which, according 

 to Cuvier, come the nearest to the Vertebrata of all articu- 

 lated animals, are nevertheless as imperfect in their organi- 

 zation, and as dull in their sensations as any in the Annulose 



