100 NORTHERN ZOOLOGY. 



INSESSORES, or PERCHING BIRDS. 



The inequality between natural groups, occupying a corresponding or analogous 

 station in their own circles, is nowhere more apparent than on looking to the 

 Insessorial birds, — the typical order of this great division of vertebrated ani- 

 mals. The Vertebrata will not bear the least comparison, in point of numbers, 

 with the Annulosa ; the proportion of the former to the latter being, in all pro- 

 bability, not more than 1 to 1 5 ; yet no one would think of denying to these divi- 

 sions an equal value in the scale of creation, merely because their contents are so 

 strikingly disproportionate. This inequality, moreover, is observable in another 

 way. It may generally be remarked, on comparing the typical with the sub- 

 typical groups, that the contents of the latter are the most numerous. But 

 sometimes this proportion is reversed, and the typical circle exhibits a greater 

 diversity of forms than are to be met with in all the other groups put together. 



The order of Insessores is of this description. It comprehends such a vast 

 assemblage of species, arranging themselves under subordinate tribes, so distinct 

 in themselves, that it becomes extremely difficult to select characters sufficiently 

 comprehensive to define the order. This difficulty, indeed, is so great, that some 

 naturalists have contented themselves with assigning negative rather than positive 

 distinctions to this order. For if we rest on their inhabiting- the land rather than 

 the water, by what reason can we exclude the Gallinaceous tribes, and even many 

 of the Grallatores, whose chief haunts are upon dry moors and commons ? The 

 Cinclus, again, is amphibious. If we characterize the Insessores as exclusively 

 perching birds, the term, rigidly understood, is equally objectionable ; for several 

 families live entirely upon the ground; while others, among the wading and 

 swimming orders, habitually repose upon trees. These, and a thousand similar 

 difficulties, have ever embarrassed the speculations of those naturalists who seek for 

 absolute and unexceptionable distinctions in nature ; where, in truth, as they do 

 not exist, so they have never been found. Without, therefore, dwelling further 

 upon such exceptions to the prominent features which characterize the order 

 before us, we may state that it is distinguished, — 



First, by the feet being of that construction most adapted for perching or grasp- 



