ARACHNID A 



181 



Fig. 114.— The Hou.se Spider 

 [Tegenaria domestica). 



View of the head seen from the front. A, 

 Head ; pp, pedipalp ; mTirf, jaw or chelicera. 



that given of the house spider in Fig. 114, in which the 



two joints of the jaws can be seen ; the sharply pointed end 



joint is able to close at will on the basal joint, like the blade 



of a clasp-knife. The jaws are moved sideways in Epeira 



and in all British spiders, 



with the single exception of 



one little burrowing form 



(Atypus), in which they 



work with an up-and-down 



motion. 



If the basal joint of one 



of these jaws or fangs is dis- 

 sected, there will be found 



inside, a poison gland, from 



which, when the spider seizes 



his prey, poison runs down 



through a narrow duct' and 



out of an opening near the 



tip of the sharply pointed terminal joint, finally entering 



the wound made by the bite and paralysing or killing the 



victim. 



The pedipalps consist mainly of the four terminal soft 



joints which act as feelers, but the basal joint next the mouth 



is hard, and functions as an extra jaw in masticating the food. 



The mouth which lies below the jaws is difficult to find, for 

 it is hidden between two fleshy pro- 

 cesses which adhere to one another 

 when the mouth is not in use. 



The under part of the 

 thorax bears four pairs of 

 seven -jointed hairy legs, coloured 

 characteristically in Epeira with dark 

 bands running across the general, 

 lighter surface. Each leg bears on 

 its end joint a pair of toothed claws, 

 below them a hooked median claw, 

 and below this again some stift' 

 serrate hairs. By means of these, 

 the spider can run along or up the 



thinnest silk thread with perfect security. On the last 



two legs, the claws can be moved to grasp things, and when 



The Thorax. 



Fig. 115. — Tarsus or Foot of 

 Epeira diademata. 



