POISONOUS INSECTS AND THEIR RELATIVES 399 



depend upon the general health of the individual injured. 

 A person in poor health may easily suffer considerable 

 pain and discomfort from the puncture or sting of an 

 insect, while another person in normal health may hardly 

 notice an equally severe attack. 



SPIDERS, THEIR VENOM AND BITES 



The biting organs of spiders consist of two rather 

 elongated jaw-like organs termed chelicerce. Each chelicera 

 is composed of two parts, or 

 segments, the base and the 

 fang. The base is rather 

 large and more or less cylin- 

 drical or conical, but the 

 fang is rather slender and 

 hook-like or claw-like. The 

 fang is connected to the 

 base by a movable joint and 

 moreover has within it a 

 small canal which opens by 

 a minute orifice near the tip 

 (Fig. 136). All spiders pos- 

 sess poison glands that con- 

 nect by minute ducts with FIG. 136. Chelicera of a spider; 



the canals in the fangs of the 

 chelicerse. The poison, how- 

 ever, is not injected into the 



wound by pressure exerted by the fang upon the gland, 

 but the gland itself is furnished with muscles, under the 

 control of the spider, that eject the poison liquid. Thus 

 it happens that a spider may or may not inject its 



p, poison gland ; d, duct ; 

 o, opening at tip of fang ; 

 /, fang ; enlarged. 



