288 FIRST PRINCIPLES OF NATURAL CLASSIFICATION. 
into, the two adjoining ones. It may, indeed, be pos. 
sible to discover a circular group without such collateral 
helps ; but the discovery is highly improbable, and it 
may be laid down as a rule that his first arrangement 
- will be more or less natural in proportion as he is 
acquainted with the objects immediately surrounding, 
or connected to, those which he is investigating. This 
plan, moreover, of making out the circular series of 
contiguous groups, is absolutely necessary for testing 
the contents of that circle more immediately under 
investigation. 
(350.) II. The second test to which our supposed 
circle must be brought, is that of analogy; in other 
words, those relations which its contents bear to the 
neighbouring circles, and to all others in its own class 
or order. It is an easy matter to place a series of 
animals in a circle, and call it a natural group, and to 
repeat the same operation with such others as come 
near to the first; but to make the contents, or divisions, 
of these circles tally with each other is a very different 
matter, and imposes a check upon the fancy which will 
dissipate many illusions. No circle whose contents 
will not bear such a comparison can be natural. It 
may, indeed, happen, that one or even two of its sub- 
divisions are wanting, while in the group with which 
it is compared they are present; yet even under these 
circumstances there will be so strong a resemblance 
between the two, in all other parts, that we may begin 
to hope our arrangement of both is correct. We should 
not, however, rest content with one or two tests of this 
sort, but bring our group, thus far safe, to encounter 
all the comparisons which we can institute. Should it 
be, for instance, the genus Picus; after tracing its 
subgenera, or divisions, in the two neighbouring genera, 
we should compare it with the sub-families of its own 
circle, and then with the families of the Scansores. If 
our arrangement is natural, we shall find parallel rela- 
tions of analogy will result from these and all other 
comparisons we make, and thus proceeding to the 
