356 



ANIMAL DEFENCES 



small poison-bag is situated at the base of each spine, and should 

 some other animal blunder against the sharp point of this, the 

 pressure causes the venom to be ejected into the wound. An 

 equally if not more effective arrangement is possessed by some 

 fishes (species of Synanceid) from the tropical parts of the Indian 



Fig. 504. — Poison Spines of Fishes 



A, Spines on tail of an Eagle-Ray (Aetobatis) (part of one drawn on larger scale at a'), b, Dorsal spine of Syjianccia', 

 p-gl. poison-bags; c, Side view of gill-cover in Tkala^sophrync. p.sp projecting tip of spine; p.gl- poison-bag 

 (exposed by dissection), c', Spine isolated, the projecting tip on right aitd bristle placed in canal. 



and Pacific oceans. Here there is a series of sharp dorsal spines, 

 of which the extremities are grooved at the sides, a small poison- 

 bag lying in each groove. Of these fishes Gunther (in The Study 

 of Fishes) says: — " The native fishermen, well acquainted with the 

 dangerous nature of these fishes, carefully avoid landing them ; but 

 it often happens that persons wading with naked feet in the sea, 

 step upon the fish, which generally lies hidden in the sand. One 

 or more of the erected spines penetrate the skin, and the poison 



