192 FISHES. 



The most perfect poison-organs hitherto discovered in 

 fishes are those of Thalassophrync, a Batraclioid genus of fishes 

 from tlie coasts of Central America. In tliese fishes the oper- 

 culum again and the two dorsal spines are the weapons. The 

 former (Fig. 100, ^) is verynarrow, vertically styliform and very 

 mobile ; it is armed behind with a spine, eight lines long, and 

 of the same form as the hollow venom-fang of a snake, being 

 perforated at its base and at its extremity. A sac covering 

 the base of the spine discliarges its contents through the 

 apertures and the canal in the interior of the spine. The 

 structure of the dorsal spines is similar. There are no secre- 

 tory glands imbedded in the membranes of the sacs ; and the 

 fluid must be secreted by their mucous membrane. The sacs 

 are without an external muscular layer, and situated imme- 

 diately below the thick loose skin which envelops the spines 

 to theu^ extremity; the ejection of the poison into a living 

 animal, therefore, can only be effected, as in Syncmceia, by the 

 pressure to which the sac is subjected the moment the spine 

 enters another body. 



Finally, a singular apparatus found in many Siluroids 

 may be mentioned in connection with the poison-organs, 

 although its function is still problematical. Some of these 

 fishes are armed with powerful pectoral spines and justly 

 feared on account of the dangerous wounds they inflict; 

 liot a few of them possess, m addition to the pectoral spines, 

 a sac with a more or less wide opening in the axil of the 

 pectoral fin ; and it does not seem improbable that it contains 

 a fluid which may be introduced into a wound by means of 

 the pectoral spine, which would be covered with it, like the 

 barbed arrow-head of an Indian. HoM'ever, whether this 

 secretion is equally poisonous in all the species provided with 

 that axillary sac, or whether it has poisonous qualities at all, 

 is a question which can be decided by experiments only made 

 with the living fishes. 



