1 and 2 afford illustrations of the excessive development of “ornament “; fig. 3 of devices for seizing the female; figs. 4 and 5 of unaccountable differences in the development of wings. 1. The Pneumatic Cricket (_Pneumora scutellaris_), showing the strange markings on the female. 2. The Cleft-footed Burrowing Cricket (_Schizodactylus monstrosus_). 3. The Giant Alder-fly (_Corydalis crassicornis_), with its huge jaws for grasping the female. 4. The Stone-fly (_Perla maxima_), the large-winged Continental form. 5. Loch Tanna Stone-fly (_Isogenus nubecula_), male, with vistigial wings. [Face page 220.] In the Locustidæ the ear is placed on the side of the front leg and the rim surrounding it may either take an oval shape or close up to form a slit. The air necessary for the efficient action of the acoustic apparatus is admitted through a gaping hole in the side of the body, above the base of the leg, an arrangement not met with among any other insects. The musical apparatus of these insects differs from that of the Acridiidæ, for it is formed only by the wing-cases, and not by the wing case and the leg. One of the wings bears a file on its inner surface, the other, the right wing, is furnished with a sharp edge placed on a prominent part of its inner margin. By slightly tilting the fore-wings, or wing-cases, and vibrating them rapidly, the edge passes under the file and a musical sound is produced. By this means one of our native long-horned Grasshoppers (_Locusta viridissima_) produces a shrill, but not unpleasant, sound, capable of being sustained continuously for a quarter of an hour. But a species encountered by Bates during his travels in the Amazons is a much more efficient performer. Known by the name of Tanana by the natives, it is so much admired by them for its singing powers that it is kept in little cages as we keep Canaries. That these organs are of importance to the species may be gathered from the case of a Bulgarian long-horned or Green Grasshopper (_Poecilimon affinis_), wherein the wings have so degenerated as to be useless in flight, but in the male they have been retained solely as musical instruments. In some species both sexes have a music-producing apparatus, but as a rule this is present only in the male. That these curious and complex stridulating organs do indeed primarily act as aphrodisiacs seems to have been clearly demonstrated by the naturalist Bates, who, in speaking of the European Field Cricket remarks: “The male has been observed to place himself at the entrance to his burrow, and stridulate until a female approaches, when the louder notes are succeeded by a more subdued tone, whilst the successful musician caresses with his antennæ the mate he has won.”