ACTIVE DEFENCE 



3SS 



gland, the secretion of which is fatal to small mammals, and suffi- 

 ciently virulent to be dangerous even to human beings. 



Actively Defensive Weapons of Amphibia and Fishes. — Re- 

 garding Amphibians, it need only be stated here that the poison- 

 glands in the skin, already spoken about (see p. 304), are in many 



Fig. 503. — Poisonous Mexican Lizard [H eloderina Jion-idinn) 



cases sufficiently potent to deserve mention under active defences 

 as well as under passive. 



Fishes are not infrequently provided with poison-spines (fig. 504) 

 of varying degrees of complexity in structure, but all serving the 

 purpose of defence. The most remarkable examples are found 

 among some of the ordinary bony forms [Teleosiei). The most 

 elaborate case is that presented by certain small ground-fishes 

 (species of Thalassophryne) from the coasts of Central America. 

 These creatures possess four sharp spines, two on the back 

 and one on each gill-cover or operculum. Each of these spines 

 is constructed on the same plan as the poison-fang of a viper, 

 being traversed by a canal which is open at the base and also 

 on one side near the tip, an arrangement which prevents blockage 

 when in use, just as in the needle of a hypodermic syringe. A 



