330 PRACTICAL AND SCIENTIFIC ZOOLOGY. 



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 Merulida, 

 or thrushes; that he has arranged them in a circle, and 

 discovered the typical and aberrant divisions. His ex- 

 position of the whole group will accordingly stand 

 thus : 



