304 INSTINCT. 



which instinct effects by one alone. Now, this maxim 

 must be taken in a qualified sense, for there are 

 instances in which instinct does vary and conform 

 to the circumstances of place and convenience. 



It has been remarked, that every species of bird 

 has a mode of nidification peculiar to itself, so that 

 a schoolboy would at once pronounce on the sort of 

 nest before him. This is the case among fields, and 

 woods, and wilds ; but, in the villages round London, 

 where mosses, and gossamer and cotton from vege- 

 tables, are hardly to be found, the nest of the 

 chaffinch has not that elegant finished appearance, 

 nor is it so beautifully studded with lichens, as in 

 a more rural district ; and the wren is obliged to 

 construct its house with straws and dry grasses, 

 which do not give it that rotundity and compactness 

 so remarkable in the edifices of that little architect. 

 Again, the regular nest of the house -martin is 

 hemispheric ; but where a rafter, or a joist, or a 

 cornice, may happen to stand in the way, the nest 

 is so contrived as to conform to the obstruction, and 

 becomes flat, or oval, or compressed. 



In the following instances, instinct is perfectly 

 uniform and consistent. There are three creatures, 

 the squirrel, the .field-mouse, and the bird called 

 the nut-hatch (sitta europ&a), which live much on 

 hazel-nuts, and yet they open them each in a dif- 

 ferent way. The first, after rasping off the small 

 end, splits the shell into two with his long fore- 

 teeth, as a man does with his knife; the second 

 nibbles a hole with his teeth, so regular as if drilled 

 with a wimble, and yet so small that one would 

 wonder how the kernel can be extracted through it ; 

 while the last picks an irregular ragged hole with 

 its bill; but as this artist has no paws to hold the 

 nut firm while he pierces it, like an adroit workman, 

 he fixes it, as it were, in a vice, in some cleft of a 



