PHYSIOPHILOSOPHICAL SYSTEMS. 349 



among the Mollusca; still, as it is equally certain that 

 this group of animals is as yet the least known, it may be 

 improper at present to conclude that it forms any excep- 

 tion to the rule : it would even seem unquestionable that 

 the Gasteropoda of Cuvier return into themselves, so as 

 to form a circular group ; but whether the Acephala form 

 one or two such, is by no means accurately ascertained, 

 though enough is known of the Mollusca to incline us to 

 suspect that they are no less subjected, in general, to a 

 circular disposition than the four other great groups.' 

 This, therefore, our author considers as one of those groups 

 which, without actually forming a circle, yet evinces a 

 disposition to do so; and it is therefore presumed to be a 

 natural group. But, to illustrate this principle farther, let 

 us return to the circle of Vertebrata. This, as we see by 

 the diagram, contains five minor groups or circles, each of 

 which is again resolvable into five others regulated pre- 

 cisely in the same way. The class Aves, for example, is 

 first divided into rapacious birds (Raptor es), perching 

 birds (Insessores), gallinaceous birds (Rasores), wading 

 birds (Gr allator es), and swimming birds (Natatores); and 

 the proof of this class being a natural group is in all these 

 divisions blending into each other at their confines and 

 forming a circle. In this manner we proceed, beginning 

 with the higher groups and descending to the lower, until 

 at length we descend to genera properly so called, and 

 reach at last the species; every group, whether large or 

 small, forming a circle of its own. Thus there are circles 

 within circles, ' wheels within wheels' an infinite number 

 of complicated relations ; but all regulated by one simple 

 and uniform principle, that is, the circularity of every 

 group." 



The writer who can see that the Quadrupeds unite with 



