= POISON GLANDS CZF 
dorsal fin is almost precisely similar to the opercular spine. 
There is no evidence as to how the poison is ejected into a 
wound, and it can only be conjectured that it may be caused by 
the pressure exerted on the gland when the spine is forcibly 
thrust for some distance into the flesh. Certain it is that these 
structures are capable of inflicting painful and troublesome 
wounds when the Fish is incautiously handled and the skin 
accidentally punctured, and no doubt they can be used with 
great effect as offensive organs. 
A similar poison apparatus exists In certain species of Batra- 
chidae, such as Thalassophryne reticulata,’ which is by no means 
uncommon at Panama. This apparatus is formed by a spinous 
outgrowth from the opercular bone and by the first two dorsal 
spines. Instead, however, of having two grooves, the opercular 
spine resembles the fang of a venomous snake, and is perforated 
by a complete canal which is only open at the base and point of 
the spine. A poison-sac at the base of the spine discharges its 
contents into the canal. The nature of the glands which secrete 
the poison has yet to be discovered, but it is probable either that 
there are glands in connexion with the poison-sac, or that the 
latter is lined by a glandular epithelium. The structure of the 
dorsal spines is similar. In some species of the Scorpaenoid 
genus Synancia * (e.g. S. verrucosa, from the Indian Ocean), the 
terminal portions of the dorsal spines are deeply grooved on each 
side, and at the origin of each groove there is a pear-shaped bag 
containing a milky poison. The bag is prolonged into a duct which, 
after traversing the groove, opens at the extremity of the spine. 
Many Siluridae are armed with powerful and often serrated 
dorsal and pectoral spines which are certainly capable of inflict- 
ing dangerous wounds, and not a few of them possess a sac-like 
organ with an external opening in the axilla of the pectoral fin. 
It is possible that the sac secretes a poison for anointing the 
spine, but at present there is no evidence that such is the case, 
or that the sac produces any poisonous secretion at all.* 
Among the Elasmobranchs the Eagle-Rays (détobatis),* and 
the Sting-Rays (7rygon), have barbed or serrated spines on the 
tail, which inflict wounds far more severe than those caused by 
1 Giinther, Trans. Zool. Soc. vi. 1869, p. 437. 
2 Thid., Study of Fishes, Edinburgh, 1880, p. 191. 
3 Ibid. p. 192. 4 Ibid. p. 190. 
VOL. Vil N 
