274 VENOMS 



This venom resists ebullition for fifteen minutes, 



V. Henri and Mdlle. Kayalof made experiments in immunisa- 

 tion. Rabbits that receive every third day increasing doses of 

 gemmiform pedicellarise of SiyhcBrecliiniis granularis tolerate well, 

 after four injections, the toxin of 40 pedicellarise, a lethal dose. 

 The serum of these rabbits is not protective for either rabbit, 

 crab, or fishes. 



Frog serum (1 c.c.) injected into the body cavity of a crab, 

 protects this animal against the pulp of pedicellariae injected 

 immediately afterwards. 



The pedicellariae easily become detached from sea-urchins. 

 They remain fixed to objects which come into contact with them, 

 and the urchin abandons them like poisoned arrows. 



On touching a point on the surface of the body of an urchin, 

 the spines are seen to incline towards the spot touched, and the 

 pedicellarise stretch themselves out and lean with their valves open 

 towards the seat of the stimulus. In SphcErechinus granularis the 

 heads of the gemmiform pedicellariae are covered with sticky mucus 

 forming a tiny drop, visible under the lens. A specimen of this 

 species possesses more than 450 pedicellarias. 



C. — Arthropods. 



(a) Araneida (Spiders). 



Almost all Arachnids possess poison-glands, which are con- 

 nected, in some cases with the buccal apparatus, in others with 

 a special inoculatory organ situated at the posterior extremity of 

 the body. The spiders and scorpions belong to this group, and 

 their venom is particularly active. 



On each side of the mouth of spiders is found an appendage 

 ending in a fang {chelicera), at the extremity of which opens the 

 excretory duct of a more or less developed poison-gland. The 

 venom produced by these glands is instantly fatal to all small 



