OCR Text |
Show 1892.] IN CERTAIN LEPIDOPTERA. 191 again pointed out, this was a structure common to all nervures, and the ribbing of the nervures is always strongest near the base of the wings. Scudder himself suggests that the sound is produced by the small erect scales on the superficies of the two wings that overlap rubbing against each other; but this is obviously inadequate to produce a clicking sound audible twenty yards off, and it is of universal occurrence that in the parts of wings that overlap the scales are short and differently formed, so as to decrease the friction ; though the rubbing of the wings one against another might be sufficient to account for the slight rustling or hissing sound made by many of the Vanessiclce when held close to the ear. Ageronia arethusa, Cram. 3 • Base of fore wing and part of thorax. a, pyriform membranous sac attached to fore wing ; b, chitinous hooks of sac; c, chitinous hooks of thorax. On detaching and clearing a fore wing of Ageronia arethusa (fig. 3), I found there was a small pyriform membranous sac attached to the base of the inner margin of the fore wing, open anteriorly, and with a pair of curved chitinous hooks with spatulate extremities lying freely in front of it. It was obvious that this could not come into contact with any of the nervures of the hind wing, and that no structure attached to the hind wing could act on it; and as there seemed to be a projection on the thorax in the immediate neighbourhood, I cleared and denuded of scales a half insect with the wings still attached to the thorax, and could then see under a low power of the microscope that there was a pair of strong chitinous hooks attached to the thorax, and that when the fore wing was moved up and down the spatulate ends of the chitinous hooks attached to the wing played against these, being released when the wing reached a certain angle, and I suggest that this is the cause of the clicking sound, the hooks acting as a tuning-fork and the membranous sac as a sounding-board. In this case the structure exists in both sexes, and we must conclude that there is a mutual wish to attract, and that perhaps it is also used as a means of inspiring fear, in accordance with Bigg-Wither's 14* |