226 STUDY OF NATURAL HISTORY. 



more particularly of perfect groups ; that is, of such 

 as exhibit, in their circular progression, no wide or 

 disproportionate gaps in their continuity. The na- 

 turalist, however, must not calculate on frequently 

 falling upon a cluster of these, so near to each other, 

 that every genus, for example, in a sub-family, shall 

 be perfect. How, then, is he to proceed, since he 

 cannot, in all instances, verify the law he has set 

 out with assuming, i. e. that every natural group is 

 circular ? He must, in this dilemma, in the first in- 

 stance, chiefly be guided by observation. Should he 

 find that, by bringing together a certain number of 

 groups, they will form a circle more or less com- 

 plete, and of a higher denomination, he may, in the 

 first instance, assume that the law in question has 

 been complied with, if not in the letter, at least in 

 the spirit. Some of the groups, thus united into one, 

 may be perfect; whereas others may contain very few 

 objects, and these objects, having distinct intervals 

 between them, form imperfect groups ; that is, they 

 present such distinct and unequal spaces in the line 

 of continuity, as to impress us with a conviction that 

 intermediate forms are wanting, to render the circle 

 perfect. Nay, it will sometimes happen that these 

 last-mentioned groups contain but two or three in- 

 dividuals, while the others comprise forty or fifty. 

 In cases like these, we must endeavour to discover 

 how far these two or three individual forms, — 

 placed together as the fragments, so to speak, of a 

 circle, — are represented in the more perfect of the 

 adjoining groups ; and by the degree of continuity 

 which these latter exhibit, estimate the extent of the 

 kiati. If these isolated forms are represented in 



