OCR Text |
Show 1892.1 IN CERTAIN LEPIDOPTERA. 189 with the sound produced. W h e n 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 Fig. 1. Mgocera tripartita, Kirby. 3- Fore leg and fore wing. 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 genus Hecatesia, 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 ASgocera, 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 different 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 |