ACTIVE DEFENCE 



355 



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 (Heloderma horridum} 



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 (Teleostei\ 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 



