VENOMS IN THE ANIMAL SERIES 297 
Their poison-apparatus is placed in the dorsal fins, as in the case 
of Scorpena and Pterois. 
2.—Trachinide. 
Genus Trachinus (Weevers).—Four species of Weevers are 
found in European seas: the Greater Weever (Trachinus draco), 
the Lesser Weever (T. vipera), the Striped-headed Weever (7. 
radiatus), and the Mediterranean Spider Weever (7. araneus) ; 
other species are met with on the coast of Chile. 
Weevers possess two sets of poison-apparatus, one of which is 
situated on the operculum, the other at the base of the spines of 
the dorsal fin (fig. 107). 
Fig. 107.—Trachinus vipera (Lesser Weever). 
The spine surmounting the operculum exhibits a double can- 
nelure connected with a conical cavity excavated in the thickness of 
the base of the opercular bone. This spine is covered with a sheath, 
beneath which lie the secreting cells. The gland is an offshoot from 
the skin, and appears as a simple follicle invaginated in the opercular 
bone (fig. 108). 
The dorsal apparatus is composed of from five to seven spines, to 
which the inter-radial membrane forms an adherent sheath which 
extends almost to the end of the rays. Each spine exhibits a deep 
double cannelure. ‘The venom flows between the layer of cells cloth- 
