PHYSIOPHILOSOPHICAL SYSTEMS.

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among the Mollusca ; still, as it is equally certain thatthis group of animals is as yet the least known, it may beimproper at present to conclude that it forms any excep-tion to the rule: it would even seem unquestionable thatthe Gasteropoda of Cuvier return into themselves, so asto form a circular group; but whether the Acephala formone or two such, is by no means accurately ascertained,though enough is known of the Mollusca to incline us tosuspect that they are no less subjected, in general, to acircular disposition than the four other great groups/This, therefore, our author considers as one of those groupswhich, without actually forming a circle, yet evinces adisposition to do so; and it is therefore presumed to be anatural group. But, to illustrate this principle farther, letus return to the circle of Vertebrata . This, as we see bythe diagram, contains five minor groups or circles, each ofwhich is again resolvable into five others regulated pre-cisely in the same way. The class Aves , for example, isfirst divided into rapacious birds {Raptores), perchingbirds ( Insessores ), gallinaceous birds ( Rasores ), wadingbirds ( Grallatores ), and swimming birds (Natatores); andthe proof of this class being a natural group is in all thesedivisions blending into each other at their confines andforming a circle. In this manner we proceed, beginningwith the higher groups and descending to the lower, untilat length we descend to genera properly so called, andreach at last the species; every group, whether large orsmall, forming a circle of its own. Thus there are circleswithin circles, ‘ wheels within wheels’—an infinite numberof complicated relations; but all regulated by one simpleand uniform principle,—that is, the circularity of everygroup.”

The writer who can see that the Quadrupeds unite with