B—On the structure of the scent organs in the maleE. core asela

Abstract

My friend, Professor Sir Edward Poulton, F. R. S., has handed me a copy of Mr. O. H. Latter’s account of his observations on the courtship of the butterflyEuplœa core asela, and the accompanying use of the scent-brushes of the male. We are deeply indebted to Mr. G. M. Henry, of the Colombo Museum, for a supply of material of the species, carefully preserved and packed, from which the sections here described have been made. As will be learned from Mr. Latter’s paper and the references therewith, special scent-organs in male insects are of frequent occurrence and have long been known. The organs inEuplœaare not of an unusual character, but Mr. Latter’s observations are entirely new, and show that the scent-apparatus is used, at least in this species,to attract the female from a distance. This function, which I venture to termtelegamic, has not hitherto been recognized except perhaps in moths of the genusHepialus, in which the action occurs over only very short distances. The scents produced by male insects have been supposed to be rather of an aphrodisiac character, coming into play only when contact, or at least proximity has been attained. Many female moths produce a directive scent, invariably, so far as is at present known, imperceptible to the human sense. Male moths will fly from great distances (experimentally for more than a mile) in response to its stimulus. Such females as have been microscopically examined do not possess special glands for the secretion of these directive odours. The whole hypodermal layer underlying the terminal segments of the abdomen is modified into a secreting epithelium, and the scent appears to be diffused by osmosis. Even among day-flying moths, sight does not appear to be an important factor in the communication of the sexes. In the majority of the butterflies, however, sight seems to be of first importance, though the butterfly’s eye is not more highly developed than is that of most moths. Whilst scent organs of considerable complexity are of continual occurrence in moths, they tend to be of a simpler character in butterflies, being usually in the form of special wing-scales which secrete a scent, frequently perceptible to the human sense. Nothing corresponding with the directive odours of female moths has so far been observed in butterflies, and of those species in which scent organs have been found, they occur only in the males, except when the odours produced are defensive, when they may be found in both sexes, as in the genusHeliconius. A high development of male scent-organs is, however, found in the Danaine butterflies, and especially in the genusAmauris, the species of which have active scentglands in the hind wings and extrusible abdominal brushes. Müller, in 1877, suggested a possible correlation between the brushes and the wing-glands, but it was not until 34 years later that the actual application of the brush to the gland was observed by Lamborn in Africa. A peculiar feature in some species is that a dust is formed by the breaking up of specially secreted fine hairs which pulverize into small particles. This dust may be formed either in the brush, as inAmauris psyttalea, or in the wing-glands, as in those species in which the gland is in the form of a pocket.