INSECTS AND THEIR NEAR RELATIVES. 



21 



segmented ; and the abdomen bears at its end organs for 

 spinning silk (Fig. 13). 



Fig. 13. — Penceiia viridans. (From the Author's Report on Cotton Insects.) 



The mandibles (Fig. 14, md) consist of two segments, 

 a strong basal one and a claw-shaped terminal one, at 

 the tip of which a poison gland opens (Fig. 

 15). It is by means of these organs that 

 spiders kill their prey. The palpi are leg- 

 like in form, but differ greatly according 

 to sex. In the female the last segment of 

 the palpus resembles a foot of the spider, 

 and is usually armed with a well-developed 

 curved claw. But in the male the corre- 

 sponding segment is more or less enlarged, 

 and very complicated in structure (Fig. 16). 

 The greater number of spiders have four 

 pairs of eyes (Fig. 17), but there may be 



Fig 



4. — Lower side 

 of cephalothorax of 

 a spider ; md, man- 

 dible; mx, maxilla; 

 />, palpus ; /, lower 

 lip; s, sternum. 



Fig. 15.— Tip of claw of Fig. 16. — Maxilla and 

 mandible of spider. palpus of male house- 



spider. 



Fig. 17.— Head of spider, 

 showing eyes and mandi- 

 bles. 



