664 



ZOOLOGY 



SKCT. 



appearance of being intermediate between the Insecta and the 

 other groups of Arachnida. The cephalothoracic region is divided 



by a constriction into two parts, 

 head and thorax, the latter made up 

 of three segments. The chelicera? 

 are chelate ; the pedipalpi resemble 

 the legs, and are used in locomo- 

 tion. The first pair of legs are at- 

 tached to the head. The abdomen 

 is distinctly segmented, and there 

 is no caudal appendage. A pair of 

 poison-glands open at the bases of 

 the chelicerse. There are two simple 

 eyes on the head. 



In the true Spiders (Fig. 543) the 

 abdomen is rounded, unsegmented, 

 and separated off from the cephalo- 

 thorax by a constriction. The chelicerse (Fig. 544, A) are sub- 

 chelate, and the duct of a large poison-gland opens at the extremity 



B 



FIG. 543. Spider (Epeira diadema). 



FIG. 544. A, Cheliceraj, and B, pjdipalpi of female of Epeira diadema. (After Leuckart.) 



The pedipalpi (Fig. 544, B) are elongated, and end in simpl 

 extremities ; in the male (Fig. 545) the terminal joint is modifier 

 to serve for the reception and trans- 

 ference of the sperms. At the ex- 

 tremity of the abdomen is the spinning 

 apparatus or arachnidiu?n (Fig. 551, 

 arach.). This consists of four or six 

 elevations, the spinnerets, sometimes 

 jointed, probably derived from em- 

 bryonic rudiments of abdominal ap- 

 pendages. On the surfaces of these 

 open the numerous fine ducts of the 

 spinning glands (sp. glds.}, secreting 

 the material of which the spider's web 

 is composed. The fine threads of viscid secretion issuing fror 

 the ducts harden on. exposure^ to the air, and are worked u 



FIG. 545. Pedipalpi of male 

 Epeira diadema. //. // 



I V. V. podomeres : bb, sac ; 

 spiral tube. (After Leuckart.) 



