leaves with its feelers. It is a wood-haunting species, and runs hither and thither over the ground as if searching for something, and pausing frequently to “purr.” This singular method of producing sound recalls that of the drumming of Woodpeckers on the hollow branches of trees, and similarly is produced without any special mechanism. That the Scorpions should possess similar stridulating organs is only what we should expect, having regard to their kinship with the Spiders. In the great Rock scorpions of India and Africa the stridulating apparatus lies between the basal segment of the pincers and that of the first pair of legs, and consists of a set of tubercles and a cluster of curved, hair-tipped spines. During moments of excitement the pincers are waved up and down so that the spinules scrape against the tubercles, emitting a rustling sound, which has been compared to that produced by rubbing a stiff tooth-brush with one’s finger-nails. In the South African _Opisthophthalmus_ the mechanism differs, consisting of leaf-like hairs placed on the inner surface of the jaws. But since both sexes possess these strange sound-producing mechanisms it has been suggested that their main, if not their only purpose, is to serve as a warning to enemies to keep their distance. Some of the great bird-eating Spiders (_Aviculariidæ_) produce a kind of whistle; others, sounds like the dropping of shot upon a plate. These stridulating contrivances present some curious and puzzling features. In the first place the sounds they produce are never loud to human ears; therein they differ from the shrill piercing sounds produced by like mechanism by the Crickets and Grasshoppers, though even with some of these the notes are, to us, inaudible. In the second, it has been suggested that where both sexes possess a stridulating apparatus its purpose is solely to warn off enemies, and this because the performers have no sense of hearing, and are thus, we presume, unaware of the sounds they produce. There is something unsatisfactory about this line of argument. There seems to be no evidence either that the sounds produced are loud enough to terrify an enemy, or that the performers are really deaf.