or have been less carefully investigated, for a comparatively limited number of insects are mentioned as possessing them. Among these are the carnivorous Coleoptera, Dytiscidæ, Silphidæ, certain Brachelytrous species, a few Diptera, &c. Notwithstanding their occasional complexity, we can for the most part discern without difficulty an apparatus for secretion, one or more deferential canals, and a reservatory bag emitting an excretory conduit which empties itself into the rectum, just above the anus. The fluids secreted are commonly colourless, and highly caustic and odorous. These properties may be easily determined by taking one of the larger Carabi and handling it roughly, when it will probably discharge the fluid, which it does with considerable force in sudden jets, and if it fall on the skin, it produces a sharp burning sensation, which however is very transient. In Carabus auratus the vessels in question consist of two branches of globular bodies, one on each side, resting on a footstalk, connected with a long deferential canal, opening into a large ovoid bladder. Chlænius velutinus (Pl. II. fig.7, a, a,) has the secreting vesicles disposed on the tops of small branchlets, so that the whole apparatus looks not unlike a branch of a willow covered with catkins. In the same fig. b is the deferential canal; c, d, the bladder. Fig. 8 in the same plate, represents these parts as they appear in the Bombardiers, a kind of beetles which have been long famous for possessing the power of producing an explosion accompanied with a discharge of smoke. This is caused by the
