II ACERATA: ARANEINA 



39; 



Legion II. Spliarogaslrida. 



Arachnida with the abdominal somites fused so that no traces of seg- 

 mentation remain. 



Order I. Araneina. 



In the spiders the soft-skinned body is divided by a deep constriction 

 into cephalothorax and abdomen (fig. 426). The four pairs of legs are 

 adapted for springing or for walking, 

 the hinder pair being also accessory to 

 the spinning. It bears a comb-like claw 

 with which several threads are combined 

 into a stronger cable. The chelicera 

 bears a sharp claw (fig. 419), traversed 

 by the duct of the poison gland with 

 which the prey is killed, although but 

 few (species oi Latrodecies, fig. 427, the 

 tarantula, and the bird spiders, Myga- 

 lids) can injure man. The pedipalpi 

 are used as feeling organs and with the 

 basal maxillary process to comminute 

 the food. In the male the pedipalpi have 

 the terminal joint swollen to a pear- 

 shaped structure (fig. 428) by which 

 the sexes are easily distinguished. This is used to convey the spermat- 

 ozoa to the female, a rather dangerous process, as the male is apt to be 

 killed by the much stronger mate. 



Fig. 426. — Epelra insularis* round- 

 web spider (after Emertcn). 



Fig. 427. Fig. 42S. 



Fig. 427. — Latrodectes madans* poison spider (after Marx). 

 Fig. 428. — Pedipalp of Pardosa uncata (after Emerton). 

 Fig. 429. — Spinnerets of Epeira diadema (after Warburton). 

 and tliird spinnerets;/, threads. 



Fig. 429. 



I, 2, 3, first, second. 



At the hinder end of the abdomen, just in front of the anus, are the 

 spinnerets, which are reduced appendages, as is shown by their paired ar- 



