Mr Adams’ second specimen was kept alive for three years and ten months. It moulted only once each year—in June or July—and it died in the act of casting its skin. In the case of these spiders, also, it was noted that insects supplied to them as food displayed no fear whatever. There were always a few cockroaches in the same box, and they were often observed actually with the spider in its nest, but no notice was taken of them unless their host chanced to be hungry. A photograph of this spider is given in the Frontispiece. It is an interesting fact that many of the Aviculariidae of Southern Asia and Australia possess a sound-producing apparatus which is entirely lacking in African and American forms, but this is a subject which deserves a chapter to itself. CHAPTER XII STRIDULATION Many of the Arthropoda—the large group which includes insects and crustaceans as well as Arachnida—are able to produce sounds, a fact familiar enough in such insects as crickets and grass-hoppers. As, however, the breathing apparatus of these animals is entirely different from that of mammals and has no connection whatever with the mouth and alimentary canal, the mode of sound production is not at all the same. Instead of setting vocal chords in vibration by the expulsion of air through the larynx, insects “sing” or “chirp” by rapidly rubbing together certain specially roughened surfaces, which constitute what is called a “stridulating organ.” In crickets, for instance, each tegmen or wing-cover is provided with a kind of file, and when the wing-covers are rapidly vibrated, the edge of each rubs against the opposite file, and a loud shrill sound is produced. The stridulating apparatus is by no means always in the same place; the thorax may rub against the abdomen, the leg against the wing-cover, or one of the mouth appendages against another. Nor are the sounds produced always audible to human ears; at all events there are many creatures with what appear to be very well developed stridulating organs whose note has never yet been heard by any naturalist, but there are doubtless numberless sounds beyond the range of our hearing, which is limited, like the keyboard of a piano. Now such a stridulating apparatus has been detected in many spiders, and always in one of three situations—either between the two parts of the body (cephalothorax and abdomen) or between the palps and the mandibles, or between the palps and the front legs. In some of the Theridiidae the hind end of the cephalothorax is roughened and fits into a sort of socket in the abdomen which is provided with parallel ridges, so that when the abdomen is vibrated the two surfaces are rubbed together, but no one has yet heard a sound produced by these spiders. The stridulating Aviculariidae, however, are easily heard, the sound in some cases being described as a kind of whistle,—in others it has been said to have the effect of shot dropping upon a plate.