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a priori, to discover some slight modifications of out- 

 ward stmcture, accordiag as the respective localities 

 differed in condition. And such we find to be every- 

 where the case. I am satisfied^ moreover, that it is 

 only by a careful observation on the spot that an insect 

 like the present one can be properly understood ; for, to 

 anybody acquainted with it practically in. all its phases, 

 it is but too evident how many ' species ' (so called) 

 might be estabhshed on undoubted varieties, where 

 there exists a desire for creating them, and where our 

 sole knowledge is gathered from a few stray specimens 

 collected by another person, and unaccompanied by local 

 information to render the aberrations intelligible. For 

 it must be tracked from the shore to an elevation of 

 more than 6000 feet before we are enabled to discern 

 the causes by which its development is controlled, or 

 even to connect by slow and easy gradations its opposite 

 extremes of form. And it is an interesting fact, that 

 the distance between its variations does not increase ia 

 proportion to the distance between its altitudes. On 

 the contrary, it would seem to pass through its minimum 

 of size and maximum of sculpture at about the elevation 

 of from 3000 to 4000 feet ; both above and below which, 

 — that is to say, as it recedes from the upper and lower 

 limits of the sylvan districts, — it becomes gradually 

 modified, and almost in. a similar manner. Thus, to a 

 person who had visited Madeira and had picked up 

 specimens on the coast, and to another who had per- 

 chance penetrated into the interior, as passing visitors 



