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Vol. XXXI. LONDON, DECEMBER, 1899. No. 12. 



BUTTERFLY WING STRUCTURE. 



BY J. ALSTON IMOFFAT, LONDON, ONT. 



Since the season of 1894 (when I first discovered that the upper and 

 lower membranes of a butterfly's wing could be separated), I have had a 

 desire to test the accuracy of the conclusions reached by me at that time ; 

 so with the remarkable profusion oi Anosia (DaJiais) Archippus, Fab., in 

 the season of 1899, I ^^^ ^t)le to secure such an abundance of material 

 to work with that I could repeat the observations until every doubt was 

 satisfactorily settled. I shall only give here a brief statement of results 

 reached, as a full account of the various processes will be published in 

 the forthcoming Annual Report of the Society for 1899. 



When a wing is fully expanded, and for an hour or two after, the 

 membranes can be easily separated. Entrance for a pin-point between 

 them is to be found at the base of the wing where the subcostal and 

 median nervures come close together. The membranes are united at 

 the costal and inner edges, which have to be cut to get them apart ; but 

 they are free at the outer angle. At that time the nervures are in two 

 parts, half in one membrane and half in the other, and open in the centre. 

 The fluid which has been stored up in the pupa enters the winglet at the 

 opening referred to, expanding the membranes as it passes along 

 between them, and the nervures at the same time, and when it has 

 extended to every portion of the wing, then it is fully expanded. The 

 expanding fluid is of a gummy consistency, and as it dries, cements the 

 membranes together, also the edges of the half-nervures, and produces 

 the hollow tubes with which we are so familiar. The photograph for the 

 plate was taken by Mr. R. W. Rennie, of this city, and is an admirable 

 example of amateur photography. 



DESCRIPTION OF PLATE 6. 



Fig. I shows the inner sides of upper and lower membranes of a front and 

 hind wing. 



