32 Trouting-Flies. 



itself almost a sufficient refutation of the ' exact 

 imitation' theory." 



I am astonished. Surely the author of 'The 

 Angler Naturalist ' does not imagine that all flies 

 of one species are of one size, any more than all fish 

 are or even all " formalists," for that matter. It is 

 true that, however long an insect may live, it never 

 grows after it has attained its perfect form ; yet 

 the growth in the larval state is not always uni- 

 form, and in the same species it is quite common 

 to find larvae of very different sizes ; and so, when 

 full development has been reached, the diversity 

 in bulk is wide enough. This is the case, more 

 or less, in all flies ; but in the green drakes, some 

 instances appear in which one fly of the species 

 is found more than double the size of another. 

 The stone-flies, too, furnish conspicuous illustra- 

 tions of such diversity; and moreover, in many 

 species of this family, as the Eev. J. G. Wood in- 

 forms us, though " there is great similitude in shape, 

 there is great difference in size between the sexes, 

 the males being scarcely one-third as large as the 

 females." x In regard to the March browns, there 

 are both large and small specimens on the water, 

 and therefore it is difficult to understand what Mr 

 Pennell means by their "natural size." I use an 

 imitation of a March brown of a "natural size," 



1 Insects at Home, p. 266. 



