1892.1 



IN CERTAIN LEPIDOPTERA. 



189 



with the sound produced. When examined with a lens, it is seen that 

 the wing-membrane is dilated so as to produce a large concavity on 

 the underside, the membrane being thrown into deep transverse 

 ridges, strongest immediately below the costa ; and when the wing is 

 cleared of scales it is seen that the costal and subcostal nervures have 

 all been distorted and curved downward, so as to give increased space 

 to the dilated and ridged membrane. The question then arose as to 

 the organ that could be used in combination with this structure to 

 produce the sound. I found that the fore tarsi, instead of being 



Mgocera tripartita, Kirby. 

 Fore leg and fore wing. 



c?- 



simply clothed with scales, or with the paired series of spines along 

 the under surface that are present in many Lepidoptera to give 

 greater power of attachment when settled, had these spines 

 immensely developed all over the upper surface of the tarsi, and 

 that if held extended, instead of folded against the under surface of 

 the body, the usual method of carrying the legs in Lepidoptera 

 during flight, the spined upper surface of the tarsi would be exactly 

 coincident with the ridged under surface of the wing-membrane, so 

 that each stroke of the wings in flight would cause the ridges 

 to pass sharply over the spines and be quite adequate, I think, to 

 produce the clicking sound. The hind tarsi have the ordinary paired 

 spines on the under surface, and I suggest that the fore tarsi can be 

 used to produce the sound, the dilated wing-membrane between the 

 ridges acting as a sounding-board, for which reason it is denuded of 

 scales on both surfaces. The use of the stridulation would be for 

 sexual attraction. 



In the closely allied ^exmsHecatesia, from Australia (fig. 2, p. 190), 

 the males have a similar but slightly modified structure ; the costal 

 edge of the fore wing is slightly folded over on the under surface of 

 the wing, and beneath this, and further from the base of the wing 

 than in Mgocera, is a still broader and more dilated area of hyaline 

 wing-membrane; this is longitudinally grooved and thrown into very 

 strong waved ridges on each side of the groove, and in correlation 

 with the diflierent position of the ridged wing-membrane we find that 

 it is the mid tarsi that have the spines strongly developed over the 



Proc. Zool. Soc— 1892, No. XIV. 14 



