The skin of the gills forms a common sheath for this defensive armature, and the base of the sheath is prolonged into two culs-de-sac, the surface of which is clothed, during the spawning season, with cylindrical cells, the secretion of which is poisonous. This venom, which is small in amount, does not appear to have any marked effect upon man (Bottard). 4.--Teuthididæ. This family of _Acanthopterygii_ includes several species of brilliantly coloured fishes with elongated and laterally compressed bodies, provided with a long dorsal fin, and having, on each side of the tail, a sharp spine placed in front of the anal fin. They are herbivorous, and are confined to the tropical seas. The principal genera are: _Teuthis_ (India), _Acanthurus_ (Tropical Atlantic), _Prionurus_ (Japan), and _Naseus_ (Red Sea and Indian Ocean). The fishermen of Réunion are much afraid of the wounds inflicted by _Acanthurus luridus_, which they call _Marguerite Porc_ or _Grande Marguerite_. A sting from this fish causes a very acute smarting pain, which may last for several hours, but usually has no serious consequences. The poison-apparatus of these fishes is situated in the dorsal and anal fins, as in _Scorpæna_. 5.--Batrachiidæ. The venomous species belonging to this family are few in number. They are found in all tropical seas, but have no representatives in Europe. The best-known species are _Batrachus tau_ (shores of Central America), and _B. grunniens_, or Grunting Batrachus (fig. 110). [Illustration: FIG. 110.--_Batrachus grunniens_ (West Indies).] [Illustration: FIG. 111.--_Thalassophryne reticulata_ (Panama; Tropical Pacific). (After Savtschenko.)] The Grunting Batrachus, which does not exceed 30 cm. in length, is especially common in West Indian waters. When taken from the water it makes a peculiar grunting sound, whence its name is derived. The pectoral fins are reddish, the back is brown, and the sides are yellow, marbled with black. It has three spines in the anterior dorsal fin, and a fourth spine on the top of the operculum, with a small poison-sac at the base of each. Next to this genus come the species of _Thalassophryne_, _T. reticulata_ (fig. 111), found on the shores of Panama, and _T. maculosa_, of Bahia (Brazil), which are provided with a precisely similar poison-apparatus. The physiological action of the venom of these two species has not yet been studied, but it is probable that it does not differ from that of the venom of the Weevers and the species of _Synanceia_. [Illustration: FIG. 112.--_Lophius setigerus_ (China Sea and Sea of Japan). (After Savtschenko.)] 6.--Pediculati.