Chap. HI. PHYSIOPIIILOSOPIIICAL SYSTEMS. 219 



these, when connected by means of five smaller osculant groups, compose the 

 whole province of Zoology.' Now these smaller osculant groups are to be viewed 

 as circles, for, as it is elsewhere stated, ' every natural group is a circle, more 

 or less complete.' This, in fact, is the third general principle of Mr. McLeay's 

 system, and he has exemplified his meaning of a natural group in the above 

 diagram, where all animals are arranged under five large groups or circles, and 

 five smaller ones. Let us take one of these groups, the Vertebrata: does that 

 form a circle of itself? Yes; because it is intimated that the Reptiles [Eeptilia) 

 pass into the Birds, [Aves,) these again into the Quadrupeds, [3Iammalia,) Quadrupeds 

 unite with the Fishes, [Pisces,) these latter with the amphibious Reptiles, and the 

 Frogs bring us back again to the Reptiles, the point from whence we started. 

 Thus, the sei'ies of the vertebi'ated group is marked out and shown to be circidar ; 

 therefore, it is a natural group. This is an instance where the circular series 

 can be traced. We now turn to one where the series is imperfect, jjut where 

 there is a decided tendency to a circle : this is the Mollusca. Upon this group 

 our author says, 'I have by no means determined the circular disposition to hold 

 good 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 exception 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 disjiositiou 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, regu- 

 lated precisely in the same way. The class Aves, for exam2)le, is first divided 

 into rapacious birds, {Rapiorcs,) perching birds, (Insessorcs,) gallinaceous birds, [liason's,) 

 wading birds, {Grallutorcs,) and swimming birds {Natatorcs) ; 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." 



