330 PRACTICAL AND SCIENTIFIC ZOOLOGY. if 
of variation. Having already explained the nature of 
the first of these proofs, we shall now give to the two 
latter a separate consideration. 
(405.) The difference between analogy and affinity 
being well understood, the naturalist is to compare his 
supposed circle with some others, which, from having 
been verified and tested in every possible manner, are 
looked upon as established. To these circular groups, 
so substantiated, he may refer as standards of au- 
thority, with which he must compare his own circle in 
all its component parts. This brings us to the appli- 
cation of the theory of analogy, by which we shall dis- 
cover that the contents of one group will represent, in 
some remarkable manner, the contents of another group. 
This representation, moreover, is not confined to a ge- 
neral similitude, nor does it rest upon one or two par- 
ticular instances, which may be selected, according to 
mere fancy, from a number of others presenting no com- 
mon similitudes; neither is it irregular, that is, the 
points of resemblance are not to be selected in an in- 
definite manner, in order to make one group tally with 
the other. No. The analogies of two groups, if they are 
natural, will occur in precisely the same order, and in 
the same succession ; and all the parts of one circle will 
represent those of another. When the student finds that 
his group will bear this test in one instance, he must 
proceed to verify it, in the same manner, by another. 
While, in proportion to the extent to which he can carry 
this comparison, and establish such similitudes or ana- 
logies between different parts of the animal kingdom, 
the greater confidence may he entertain that his circle 
is truly natural. 
(406.) Let us now illustrate this precept by an ex- 
ample. We will suppose the student to have investigated 
the family of birds just mentioned, viz. the Merulide, 
or thrushes; that he has arranged them in a eircle, and 
discovered the typical and aberrant divisions. His ex- 
position of the whole group will accordingly stand 
thus : — 
