The two British species of "Weever" (_Trachinus draco_ and _T. vipera_) are both provided with poison-organs in connexion with a spine on the operculum and with the five or six spiny rays of the anterior dorsal fin.[151] The first of these spines is a structure projecting backwards from the hinder margin of the opercular bone of the gill-cover, and is traversed along both its upper and lower margins, from base to point, by a deep groove. Except at its protruding naked point the spine is ensheathed in an extension of the external skin. Along each of the grooves there extends a solid pear-shaped mass of gland-cells, the broad base of which coincides with the base of the spine, while the gradually tapering, narrower portion is continued as far as the sharp point. The glands enclose no cavity, and there is no duct, so that whatever poisonous fluid their cells secrete is probably set free by the rupture of the cells and discharged into the grooves, along which it passes to the point of the spine, somewhat after the fashion of a hypodermic syringe. The origin of the gland-cells from an in-pushing of the epidermis is indicated by the continuity of the two structures near the point of the spine. Both in structure and in their relation to poison-glands each of the spines of the {177}dorsal fin is almost precisely similar to the opercular spine. There is no evidence as to how the poison is ejected into a wound, and it can only be conjectured that it may be caused by the pressure exerted on the gland when the spine is forcibly thrust for some distance into the flesh. Certain it is that these structures are capable of inflicting painful and troublesome wounds when the Fish is incautiously handled and the skin accidentally punctured, and no doubt they can be used with great effect as offensive organs. A similar poison apparatus exists in certain species of Batrachidae, such as _Thalassophryne reticulata_,[152] which is by no means uncommon at Panama. This apparatus is formed by a spinous outgrowth from the opercular bone and by the first two dorsal spines. Instead, however, of having two grooves, the opercular spine resembles the fang of a venomous snake, and is perforated by a complete canal which is only open at the base and point of the spine. A poison-sac at the base of the spine discharges its contents into the canal. The nature of the glands which secrete the poison has yet to be discovered, but it is probable either that there are glands in connexion with the poison-sac, or that the latter is lined by a glandular epithelium. The structure of the dorsal spines is similar. In some species of the Scorpaenoid genus _Synancia_[153] (e.g. _S. verrucosa_, from the Indian Ocean), the terminal portions of the dorsal spines are deeply grooved on each side, and at the origin of each groove there is a pear-shaped bag containing a milky poison. The bag is prolonged into a duct which, after traversing the groove, opens at the extremity of the spine.