VERIFICATION OF GROUPS. 287 
mary types explained in the preceding pages. If, in — 
short, a zoological group be natural, it will not only 
bear a comparison with every other in the same class, | 
but will give and receive a flood of light to and from — 
all with which it is compared. 
(348.) It fellows, from the preceding remarks, that 
the verifications of a natural group are three: 1. The 
circular series of its contents; 2. The parallel rela- 
tions of its parts to other groups; and, 3. The sym- 
bolical representation of the primary types of nature. 
On some of these points we have expatiated *; but this 
is the proper place for treating the subject in a more 
definite, clear, and connected manner. 
(349.) There are no absolute rules, of universal ap- 
plication, independent of analysis, which can be laid 
down for the discovery of a zoological circle. We 
must begin, in fact, by arranging the objects with the 
nicest attention to their apparent affinities, and then 
testing the result. If these affinities are real, and the 
group is natural, there will be an evident tendency to a 
circle ; and this tendency will be more or less strong, in 
proportion to the number of objects which enter into the 
series. When we consider, however, that the relations of 
objects are complicated, and by no means confined to those 
which precede, or these which follow them, in the series 
of affinity, it is obvious that false circles may be made ; 
and that their fallacy can only be discovered by further 
tests. Before the naturalist proceeds to these, it is 
absolutely necessary that he endeavours to make out 
the two immediate circles which pass into that with 
which he has first begun. If, for instance, he was 
investigating the genus Picus Sw., as now constituted, 
after simply tracing the circular affinities of this group, 
he should proceed to investigate the two others which 
more immediately join it; namely, Chrysoptilus Sw. 
and Melanerpes. Unless this were done, he will have 
no definite ideas on the probable demarcation of his 
first circle, at those points where it touches, and passes 
* Preliminary Discourse on Nat. Hist. 
