104 



NATURAL HISTORY OF ARTHROPODS. 



FIG. 143. Foot of Epelra vulgaris. 



duction, and the spinning-organs. Connected with the thorax are six pairs of limbs - 



four pairs of legs, a pair of palpi, and a pair of mandibles. 



The legs are used chiefly for running, jumping, and climbing; but the front pair 



serve often as feelers, being held up before the body while the spider walks on the 



other six. One or both of the hinder legs are used 

 to guide the thread in spinning ; the spider at the 

 same time walking or climbing about with the other 

 six or seven. The legs are seven-jointed, and on 

 the terminal joint are three claws and various hairs 

 and spines. In many spiders a brush of hairs takes 

 the place of the middle claw, as in the jumping 

 spiders. Spiders with these brushes on their feet 

 can walk up a steep surface, or under a horizontal 

 one, better than those who have three claws. 



In front of the legs are the palpi a smaller 

 pair of limbs, with six joints and only one claw or 

 none. They are used as feelers and for handling 

 food, and, in the males, carry the curious palpal 

 organs, which will be described farther on. The 



basal joints of the palpi are flattened out and serve as chewing-organs, called maxilla?. 

 The first pair of limbs, the mandibles or cheliceraj, are two-jointed. The basal 



joint is usually short and stout, and furnished on the inner side with teeth and hairs. 



The terminal joint is a small and sharp claw, which 



can be closed against the basal joint when not in 



use. 



On the under side of the abdomen, just behind 



the last pair of legs, are two hard, smooth patches 



which cover the front pair of breathing-organs, the 



openings to which are two little slits, or stigmata. 



Between these is the opening of the reproductive 



organs, and, in female spiders, the epigynum, an 



apparatus for holding the reproductive cells of the 



male. 



At the end of the body are the spinnerets. There 



are three pairs of them ; but many spiders close them 



together when not in use, so as to cover np the middle 



pair. The third pair of spinnerets are often several- 

 jointed, and extend out behind the body like two tails. 



In front of the spinnerets is a spiracle which leads to air-tubes which give off branches 



to different parts of the abdomen. 



Turning now to the dorsal surface, on the front of the head are eight eyes which 



are differently arranged in different spiders. At the back part of the thorax is a 



groove, beneath which is attached a muscle for moving the sucking-stomach. On the 



abdomen are several pairs of dark, smooth spots, which mark the ends of muscles 



extending downward through the abdomen. 



d? tj 



The mouth is just under and behind the mandibles, and between the maxillae. It 

 has an upper and an under lip, each lined with a horny plate, in the middle of which 

 runs a groove. When the lips are closed the two grooves form a tube which leads to 



\ 



FIG. 144. Foot of Attus mystaceus. 



