244 STUDY OF NATURAL HISTORY. 



stated, are seen to put on so many different forms. 

 Yet, although we are unable to employ these variable 

 peculiarities in a primary sense, they afford ad- 

 mirable distinctions of a secondary nature ; and 

 these, when coupled with the peculiar formation of 

 the wing common to the whole group, give us a com- 

 pound of characters by which all titmice warblers 

 may be distinguished, almost at a single glance, 

 from the hundreds of species composing the family 

 Sylviadce. 



(168.) Now if, in proceeding to the investigation 

 of another genus, we find that also characterised, as a 

 whole, by some one peculiarity of structure ; and that 

 it also comprehends subordinate forms, more or 

 less agreeing with those in the last ; we have every 

 solid reason to suppose these subordinate forms, in 

 both groups, to be analogous ; or, in other words, 

 to represent each other. To give them, therefore, 

 discriminating characters, we unite that of the 

 entire genus to that of the sub-genus, as before 

 intimated ; and these, collectively, give us a distin- 

 guishing formula, by adhering to which we cannot 

 possibly err. 



(169.) Of natural groups, Linnaeus certainly had 

 a very sound theoretical idea, when he said, that 

 every genus would furnish its own characters, and 

 not that the characters should form the genus ; 

 thereby implying, that we were first to place objects 

 together which appeared closely related, and then 

 to discern what were the peculiar and tangible 

 characters which made them so. The truth is, 

 that, generally speaking, an unscientific person, but 

 with a discriminating eye, is much more likely to 



