298 ENTOMOLOGY FOR MEDICAL OFFICERS 



Order Araneida : Spiders (Lat. araneus = s. spider). 



In this, the largest order of Arachnida, the body is 

 composed of a well-chitinised cephalothorax, which carries 

 the true appendages, and of an abdomen, which is usually 

 soft and unsegmented, and is attached to the cephalothorax 

 by a short stalk. The integument is more or less hairy. 



Ventrally the cephalothorax shows distinct segmentation 

 in the attachment of the appendages and the subdivision of 

 the sternum ; but dorsally it is covered by a carapace which 

 at most shows only traces of segmentation. On the carapace 

 are the eyes, which commonly are eight in number and are 

 arranged, more or less distinctly, in two rows. 



The first pair of appendages, or chelicercB, are the poison- 

 fangs with which spiders kill their prey. They consist of 

 two pieces — a basal piece containing the poison-gland, and 

 a large curved claw which is perforated near the tip to give 

 exit to the venom, after the manner of a snake's fang. 



The second pair of appendages, or pedipalps, resemble 

 the legs, except that their basal segment is produced to form 

 a maxillary process. In the adult male the terminal segment 

 of the pedipalps is swollen, and is modified for transferring 

 the sperm to the female. 



The legs, which are four pairs, consist of 7 segments and 

 end in two, or three, claws. In those spiders that possess 

 an accessory spinning-plate, or cribellum, the protarsus of 

 the hind legs carries a special comb of hairs, or calamistnmt, 

 which is used for fashioning the threads secreted from the 

 cribellum. 



The abdomen, typically, is soft, globular, and un- 

 segmented, but sometimes is horny and angular, or festooned, 

 or spinose, or is very rarely segmented. On its ventral 

 surface, as a rule posteriorly, just in front of the anus, are 

 the spinnerets, of which there are commonly three pairs, 

 but sometimes two pairs, or one pair, or very rarely four 

 pairs. The spinnerets, which are regarded as modified 

 appendages, are segmented and mobile, and are perforated 

 at tip by the numerous fine openings of the spinning-glands. 

 Some spiders have, in front of the ordinary spinnerets, a 

 broad spinning-plate, or cribellum. The spinning-glands 



