NATURAL SYSTEMS. MACLEAY. 205 



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 pre- 

 sumed to be a natural group. But, to illustrate this 

 principle farther, let us return to the circle of VERTE- 

 BRATA. This, as we see by the diagram, contains five 

 minor groups, or circles, each of which is again resolv- 

 able into five others, regulated precisely in the same way. 

 The class Aves, for example, is first divided into ra- 

 pacious birds (Raptores), perching birds (Insessores), 

 gallinaceous birds (Rasores), wading birds (Grallatores), 

 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.f 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 circu- 

 larity of every group. 



(260.) We must return, however, to thenumber of divi- 

 sions of which our author considers every natural group is 

 composed ; because on this point he appears not strictly 

 consistent with himself. We have seen, in the forego- 

 ing diagram, that the first division of the animal king- 

 dom are resolved into ten circles or groups, five large 

 and five small. In the following passage, however, 

 when speaking of this diagram, Mr. MacLeay seems to 

 lose sight of these lesser circles, and reckons the larger 



* Hor. Ent. p. 322. 



f First pointed out by Mr. Vigors, Linn. Trans. 



