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VII. The condition of the scales in the leaden males of 

 Agriades thetis, Rott., and in other Lycaenids. By 

 E. A. Cockayne, D.M., F.R.C.Pi, Temporary 

 Surgeon, R.N. 



[Read March 7th, 1917.] 



Plate XI. 



The peculiar colour of the leaden males of Agriades thetis, 

 many of which were taken near Folkestone in 1916 and 

 occasional specimens in previous years, led me to think 

 that a microscopical examination of their scales might be 

 of considerable interest. 



In the normal male thetis the wing is covered with lines 

 of smoky scales, short and broad, which have strong 

 longitudinal ribs and well-marked cross striations. Alter- 

 nating with the rows of dark scales are rows of longer 

 scales, which I call for convenience the " colour scales." 

 These are also longitudinally ribbed, but have weaker 

 cross striation, and are yellow by transmitted light and 

 brilHant blue by reflected light. The blue colour has 

 generally been regarded as an interference colour due to 

 the cross striae and not a pigmentary colour, but H. M. Sims 

 (Canadian Entomologist, 1915, p. 161) considers that it 

 is dependent on a fluorescent dye. In either case the 

 dark scales serve to absorb any light which passes through 

 the blue scales, and to prevent the coloured scales on 

 the underside of the wing from being visible on the 

 upperside. 



In addition to these two kinds of scales small colourless 

 androconial scales are present in abundance. In the leaden 

 males of thetis, the smoky scales and androconia are of 

 normal shape, size and colour, but all the colour scales 

 are very thin, and have their distal part rolled up to form 

 a tube. By reflected light the curled-up edges and tubular 

 ends of these scales look silvery, and under a low power 

 of the microscope appear as ghostly triangles overlying 

 the dark scales, which are much exposed to direct view 

 and give the leaden colour to the wings. 



TKANS. ENT. SOC. LOND. 1917. — PART I. (nOV.) 



