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 appearance of being circular, — it is 

 plain that there must be something wrong in our 

 p 4 



