ORDER OF SUCCESSION. 215 
perceive, without investigation, that they are of 
analogy; but in proportion as groups approximate, 
other dissimilarities of course become less, so that 
when we descend to genera which follow or come 
very close to each other, it is impossible to decide, 
at first sight, whether the relationship be one of 
analogy or of affinity. But of this hereafter. 
(151.) As every group, therefore, is found to 
contain some such striking modifications of form, it 
becomes necessary to ascertain how far they follow 
each other, in the same succession, in each group: 
for it is not to be supposed that they occur at 
random, or that they merely constitute a part of 
their own group, without having any uniform and 
definite station therein. The series of variation in 
one, must be the same in all. When, therefore, we 
wish to verify an assumed circle of affinity, our first 
business is to study the order of succession in which 
the subordinate forms in it occur, and then to com- 
pare it with other assumed circles. The proof that 
our arrangement of one is correct, is involved in the 
general verification of the whole. If the succession 
of forms in one and all of these circular groups 
agree, we can then have little or no doubt, that 
the order of nature has been discovered; for we 
shall then arrive at one general principle of variation, 
and shall be able to assign to each form the station 
it holds in its own group. If, on the other hand, 
we find no such analogy between the contents of 
our groups —if they contain no corresponding re- 
presentations —and if they rest for their stability 
upon the mere appqarance of being circular, — it is 
plain that there must be something wrong in our 
PA 
