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same species as those of Great Britain, exhibit small 

 local characteristics by which they may be immediately 

 distinguished, — such as the length of the wings, size of 

 the bills, and tints of the plumage. So that the migra- 

 tory birds generally, which pass to and fro between 

 Europe and Africa in that particular latitude, would appear 

 to form separate races from those which traverse the 

 ocean to our own country; and to be, most of them, 

 remarkable, inter alia, for a slight shortening of their 

 organs of transit. 



If, however, the members of the insect tribes are 

 capable of but small variation in actual structure, with 

 the exception, in certain instances, of the greater or less 

 development of the wings ; we shall find that their ex- 

 ternal characters are much more prone to instability. 

 There is not an item indeed of all their secondary 

 diagnostics wliich does not admit of a positive change ; 

 and, though it be only within fixed limits that the 

 several modifications can occur, those boundaries are 

 frequently far apart, and include at times numerous 

 phases within their embrace which have been too often 

 looked upon as specific. Thus, whether we regard their 

 bulk, outline, colour, or sculpture, anything like absolute 

 constancy, imder aU circumstances and conditions, does not 

 so much as exist ; and we are driven to admit, that the 

 physical influences to which these various creatures are 

 exposed have a very decided power over their general 

 configuration and aspect. It would be needless, however, 

 to attempt to discuss the above details of aberration 

 separately ; because, where any one of them is especially 



