INSECTS AND THEIR NEAR RELATIVES 



The cephalothorax is also unsegmented ; and the abdomen bears at its 

 end organs for spinning silk (Fig. n). 



The cheliceras (Fig. 12, 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. 13). It is by 

 means of these organs that spiders 

 kill their prey. The pedipalpi are 

 leg-like in form, but differ greatly 

 according to sex. In the female 

 the last segment of the pedipal- 

 pus resembles a foot of the spider, 

 and is usually armed with a well- 

 developed curved claw. But in 

 the male the corresponding seg- 

 ment is more or less enlarged, and 

 very complicated in structure 

 (Fig. 14). The greater number of 

 spiders have four pairs of eyes, but 

 there may be only one, two, or 

 three pairs; and certain cave 

 spiders are blind. Spiders breathe by means of lung-sacs, of which there are 

 one or two pairs ; and some have tracheae also. The lung-sacs open on the 



Fig. 11. — The banana spider showing division of body 

 into cephalothorax and abdomen. 



Fig. 12. — Lower side 

 of cephalothorax of a 

 spider; md, chelicera; 

 mx, maxilla; p, paipus; 

 /, lower iip; s, sternum. 



Fig. 13. — Chelicera of a spider: p, 

 poison gland; d, duct; o, opening at 

 tip of fang; /, fang. 



Fig. 14. — Maxilla 

 and palpus of male 

 house-spider. 



Fig. 15. — End of abdomen 

 of spider, showing six spinn-r- 

 ets spread apart; in front of 



lower side of the abdomen near its base, 

 and between them is the opening of the 

 reproductive organs . The tracheae open 

 through a single spiracle near the hind 

 end of the body, usually just in front 

 of the spinning organs. 



The spinning organs, which are sit- FlG l6 _ A Rroup 

 these'^Thesp^cie.'and'behind uated near the end of the abdomen, of spinning tubes, 

 them the opening of the aiimen- CO nsist of one or two or three pairs of gI 



tary canal. . l , . . 



spinnerets. These appendages (tig. 15) are more or 

 less finger-like in form, and sometimes jointed. Upon the end of each spin- 

 neret there are many small tubes, the spinning tubes, from which the silk is 

 spun (Fig. 16). Some spiders have one hundred or more of these spinning- 



