176 FISHES CHAP. 



Poison Glands of Fishes. 



A few Teleosts are provided with weapons of offence or 

 defence in the shape of poison-glands, probably derived from the 

 epidermis, and associated with spines on the gill-covers, or in 

 connexion with the dorsal fin, or with both. 



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.^ 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 



Fig. 95. — The opercular spine of Trachinus draco and its poison-glands, cr, Articula- 

 tion of the opercular bone with the hyomandibular ; gl.gl, the two poison- 

 glands ; op.m, opercular membrane ; op.s, opercular spine ; r, outer ridge of the 

 spine ; sk, sheath of the spine. (From W. Ne\vton Parker.) 



its protruding naked point the spine is ensheathed in an exten- 

 sion 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 what- 

 ever 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 

 1 W. Newton Parker, P.Z.S. 1888, p. 359. 



