FAM. 60. ELATERIDAE (_Click-beetles_).—_Antennae more or less serrate along the inner margin, frequently pectinate, rarely filiform. Front coxae small, spherical. Thorax usually with hind angles more or less prolonged backwards; with a prosternal process that can be received in, and usually can move in, a mesosternal cavity. Hind coxa with a plate, above which the femur can be received. Visible ventral segments usually five, only the terminal one being mobile. Tarsi five-jointed._ This large family of Coleoptera comprises about 7000 species. Most of them are readily known by their peculiar shape, and by their faculty of resting on the back, stretching themselves out flat, and then suddenly going off with a click, and thus jerking themselves into the air. Some, however, do not possess this faculty, and certain of these are extremely difficult to recognise from a definition of the family. According to Bertkau[133] our British _Lacon murinus_ is provided near the tip of the upper side of the abdomen with a pair of eversible glands, comparable with those that are better known in Lepidopterous larvae. He states that this Insect does not try to escape by leaping, but shams death and "stinks away" its enemy. The glands, it would appear, become exhausted after the operation has been repeated many times. The extent of the leap executed by click-beetles differs greatly; in some species it is very slight, and only just sufficient to turn the Insect right side up when it has been placed on its back. In some cases the Insects go through the clicking movements with little or no appreciable result in the way of consequent propulsion. Although it is difficult to look on this clicking power as of very great value to the Elateridae, yet their organisation is profoundly modified so as to permit its accomplishment. The junction of the prothorax with the after-body involves a large number of pieces which are all more or less changed, so that the joint is endowed with greater mobility than usual; while in the position of repose, on the other hand, the two parts are firmly locked together. The thoracic stigma is of a highly remarkable nature, and the extensive {258}membrane in which it is placed appears to be elastic. Although the mechanics of the act of leaping are still obscure, yet certain points are clear; the prosternal process possesses a projection, or notch, on its upper surface near the tip; as a preliminary to leaping, this projection catches against the edge of the mesosternal cavity, and as long as this position is maintained the Insect is quiescent; suddenly, however, the projection slips over the catch, and the prosternal process is driven with force and rapidity into the mesosternal cavity pressing against the front wall thereof, and so giving rise to the leap.