260 STUDY OF NATURAL HISTORY. 



of rapacious birds may be used as a subordinate 

 mark of discrimination, if accompanied by deviations 

 in structure, yet not otherwise. The nature of the 

 ordinary food of an animal is almost always indicated 

 by its external organisation. We know by experience 

 that certain habits of life are indicated by certain 

 peculiarities of form, so that by studying the con- 

 formation of an animal which we have never seen 

 alive, we can arrive, with a degree of certainty 

 almost incredible, at a general knowledge of its 

 habits and economy. This is more particularly the 

 case among birds ; because, perhaps, they have 

 been more especially studied with reference to these 

 circumstances than any other class of animals. In 

 these the form of the bill is of as much importance 

 in determining the food, as are the teeth of quadrupeds 

 or the jaws of insects. Purely insectivorous birds 

 must always be considered as of a different type to 

 such as partake more or less of vegetable food, even 

 should such deviations be found in the same sub- 

 family or even genus. A singular instance of this 

 occurs in the sub-family of the Titmice (Parlance). 

 All these birds live entirely upon insects excepting 

 one genus, that of Accentor, to which belongs our 

 common hedge-sparrow: this bird, as every one 

 knows, feeds as much upon small seeds as upon 

 minute insects ; yet it is so intimately and un- 

 questionably related to the group it has been placed 

 in, that the perfection and unity of the whole divi- 

 sion would be destroyed, if, because it was not 

 purely insectivorous, we took it out of the circle, and 

 endeavoured to find a place for it elsewhere : never- 

 theless, we still make use of this peculiarity of habit 



