Of the fishes belonging to this family, the species of the genus _Muræna_ alone concern us. They have an elongated body, without pectoral fins, and a naked skin, covered with a thick layer of viscid slime, as in the case of the eels. Their dentition is powerful, formed of long, recurved fangs, arranged in one or more rows. These fishes may attain a large size, exceeding 2 metres in length. More than one hundred species are known, all of which live in tropical or subtropical seas. _Muræna helena_ is common in the Mediterranean in the vicinity of Nice and Toulon; _M. moringa_ (fig. 120) is found in the Tropical Atlantic. The species of _Muræna_ live in deep water, and feed upon fishes or crustaceans. In hot countries they frequently venture into fresh water. Their skins are adorned with brightly coloured markings, which vary very greatly according to the species. The poison-apparatus in _Muræna_ consists of a pouch situated above the membrane of the palate, which may contain ½ c.c. of venom, and three or four conical, curved teeth, with the convex surface in front, as in the fangs of snakes. The teeth are not pierced by a central canal, and the venom flows between them and the mucous membrane of the palate, which forms a sheath. The latter is withdrawn to the base of the teeth, while they are penetrating the tissues. The teeth are mobile; they are articulated with the palatine bone, in which they are inserted in small depressions, and a resistant fibrous tissue serves as the means of union. They can be deflexed backwards against the mucous membrane of the palate; in this position the first, second and fourth tooth (when the latter exists) disappear completely between the folds of the membrane. The third tooth normally remains erect, and it is this by which wounds must in most cases be inflicted. None of these teeth can be protruded beyond the vertical. [Illustration: FIG. 120.--_Muræna moringa_ (Tropical Atlantic). (After Savtschenko.)] In addition to the palatine teeth there are, among the groups of maxillary teeth, several mobile teeth, which are connected with the poison-reservoir. Besides its toxic action the venom of _Muræna_ has manifest digestive properties, and, in the case of a fish which has been dead for some little time the gland is no longer to be found, since its walls have undergone a rapid autodigestion. The venoms of all the fishes of which I have just given a brief description, as regards their physiological action, present a fairly close resemblance to the venom of the Weever, and show scarcely any variation except in the intensity of their effects. They have been but little studied hitherto, and it is desirable that they should be better understood. CHAPTER XVIII. _VENOMS IN THE ANIMAL SERIES_ (_continued_). 3.--_BATRACHIANS. LIZARDS. MAMMALS._ A.--Batrachians.