BUTTERFLIES-MOTHS. 73 trouve mal à son aise, qu'il crie; il crie dans les poudries, dans les boistes où on le tient renfermé; ses cris redoublent lorsqu'on le prend, et il ne cesse de crier tant qu'on le tient entre les doigts. En général il fait grand usage de la faculté de crier, que la nature lui à accordée." * There has been much doubt how the sound arises, but it appears to be ascertained that the moth produces it by rubbing the palpi against the base of the proboscis.† Huber thought, and subsequent writers-as, for instance, Kirby and Spence, and Bevan-have concurred in the opinion, that the sound "operates on the bees like the voice of their queen, and thus enables the moth to commit the greatest ravages in the hives with perfect immunity." On the other hand, Huber ascertained by experiment that it exercises no such charm over humble bees. Several other species of the genus Sphinx also produce a sound, and a few other moths, for instance, Noctua fovea. Darwin also mentions § a Brazilian butterfly, Ageronia feronia, as making "a noise like that produced by a toothed wheel passing under a spring catch, which could be heard at the distance of several yards.' The peacock butterfly (Vanessa io) || is also said to possess the same power. For further details with reference to the sounds produced by insects, and, indeed, by animals generally, * "Mém. p. servir à l'Histoire des Insectes." + Landois, "Die Ton und Stimm Apparate der Insekten," Zeit. für Wiss. Zool., vol. xvii. Bevan, "On the Honey Bee." § "Descent of Man,” vol. i. Zool., 1867. 74 CENTIPEDES-SPIDERS. I may refer to Landois's interesting work, "Thierstimmen." From the fact that the power of producing sounds audible to us is scattered among so many groups, and that the sounds themselves are often so shrill, I am disposed to suspect that many insects usually regarded as dumb really produce sounds, which, however, are beyond our range of hearing. Among centipedes Gerstäcker has described* a sound-producing organ in Eucorybar crotylus. The posterior legs have the fourth segment much enlarged and leaf-like, with the edges raised and formed of very hard chitine. The legs are rubbed against one another, and thus produce a rasping sound. Bourne also has recently described† a stridulating organ in another genus (Sphærotherium). It is situated just behind the twenty-first pair of legs, and consists of a hood-like process bearing a number of parallel ridges. There is a very general impression that spiders hear well, and even enjoy music! There seems, however, very little evidence of any value on the subject. No doubt they are extremely sensitive to vibrations. The presence of even a very small insect on their web is at once perceived. Mr. Boys has shown that the vibrations of a tuning-fork affect them strongly.‡ This sensitiveness to vibrations is, however, not necessarily the same as a true sense of hearing. Kraepelin says that he knows only one observation which seems. to him to possess sufficient exactness to justify the conclusion that spiders possess any sense of hearing— namely, that of Lehmann. * Gerstäcker, "Stettin Ent. Zeit., 1854. † Bourne, Linnean Journal, 1885. Nature, vol. xxiii. § "Ueber die Geruchsorgane der Gliederthiere." POWER OF HEARING IN INSECTS. 75 It would be, on the other hand, most unsafe to conclude that spiders are incapable of hearing. Dahl* has given reasons for believing that some of their hairs serve as auditory organs. Westring has discovered, in certain species of Theridium (T. serratipes, oculatum, castaneum, etc.), a stridulating organ, consisting of a sort of raised bow attached to the upper part of the abdomen, which rubs against the under and hinder part of the cephalothorax, producing a whirring sound. Lebert † naturally observes that this appears to indicate a power of hearing on their part. As regards insects, it would be easy to multiply such evidence almost indefinitely; I have given more illustrations than I should probably have otherwise thought necessary, because so excellent an observer as Forel, whose opinion I should value on such a point as much as that of any authority, expresses doubt whether insects really hear at all. "Ce qu'on semble," he says, in his last memoir on the subject, "considérer comme preuve de l'ouïe me paraît comme à Dugès reposer à peu d'exceptions près sur des ébranlements mécaniques de l'air ou du sol qui sont simplement perçus comme tels par les organes tactiles des insectes. Cela correspond à peu près à la dernière opinion de Graber sur" l'ouïe "de la Periplaneta. Mais on n'a pas le droit de nommer ouïe de pareilles sensations." ‡ Graber, however, has endeavoured to meet this objection by an ingenious experiment.§ He placed some water-boatmen (Corixa) in a deep jar full of * "Das Gehör-und Geruchsorgane der Spinnen,” Arch. für Mic. Anat., 1885. "Die Spinnen der Schweiz." A. Forel, "Sensations des Insectes," Recueil Zool. Suisse, t. iv. 1887. § Arch. für Mic. Anat., 1882. 76 SENSE OF HEARING IN INSECTS. water, at the bottom of which was a layer of mud. He dropped a stone on the mud, but the beetles, which were reposing quietly on some weeds, took no notice. He then put a piece of glass on the mud, and dropped the stone on to it, thus making a noise, though the disturbance of the water was the same. The water-boatmen, however, then at once took flight. In face of all the evidence, then, I do not think there can reasonably be any doubt on the subject, and it seems to be clearly established that insects do possess the sense of hearing. ( 77 ) CHAPTER V. THE ORGANS OF HEARING. THAT many of the lower animals have special organs for the production of sound, and possess the sense of hearing, has been shown in the preceding chapter. I now proceed to consider the mechanism by which sounds are perceived. In our own ear we have, first of all, the external ear, much less important in man than in many other animals, as in the horse, for instance, where it may be seen moving continually, and almost automatically assuming the position most favourable for conveying the waves of sound down the outer passage (Fig. 46, D) to the tympanum, or drum. This is a membrane stretched between the outer air on the one hand, and the drum on the other, which also contains air, transmitted through the mouth by means of the Eustachian tube (Fig. 46, E). The drum is separated from the brain by a hard, bony partition in which are two orifices, one oval and the other round. Across the drum stretches a chain of little bones (Fig. 47); first the "hammer," secondly the "anvil," and lastly the "stirrup." The flat plate of the stirrup, again, lies against the oval orifice, or fenestra ovalis, as it is technically called, of the drum. Thus the sounds are intensi |