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 ” (Zrachinus draco and 7. 
vipera) ave 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 
Fic. 95.—The opercular spine of Trachinus draco and its poison-glands. a7, Articula- 
tion of the opercular bone with the hyomandibular ; g/.g/, the two poison- 
glands ; op.m, opercular membrane ; op.s, opercular spine; 7, outer ridge of the 
spine ; sh, sheath of the spine. (From W. Newton Parker.) 
its protruding naked point the spme 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. 
Fs. 
