ON SUB-FAMILIES. 221 



arrangement, the greater is the probability of our 

 discovering the order of nature, it becomes essential 

 to ascertain how far the laws regarding the com- 

 bination of sub-genera into genera will assist us to 

 combine genera into sub-families. We have sup- 

 posed in the latter case, that the naturalist has found, 

 in all his perfect genera, the prevalence of a deter- 

 minate number of minor divisions; he is now, 

 therefore, to try the strength of the law thence as- 

 sumed, upon a more extensive scale. First, we must 

 combine our genera in such a way that four, five, 

 seven (or whatever the assumed number may be), 

 make a circle of their own, more or less complete. 

 We shall then have a certain number of circular 

 groups, forming one of larger dimensions ; and, pro- 

 ceeding in this way to form other assemblages of 

 the same kind or rank, compare their respective 

 contents. The first test of every such circle will be 

 that its primary divisions or genera are also circular : 

 the second, that these divisions or lesser circles, in 

 regard to their number, are definite. If we find 

 that their average number is greater or less in the 

 sub-families, than in the genera, we must conclude 

 one of two things ; either that the number of types 

 vary in different groups according to the rank or 

 value of such groups, or that we have not yet dis- 

 covered what is the true number most prevalent in 

 nature. Every principle of sound reasoning is 

 against the first of these suppositions ; for if we 

 suppose that natural groups are perfectly independ- 

 ent of any definite number of divisions, then (setting 

 aside all experience to the contrary) we virtually 

 deny uniformity of design in the details of nature, 



