116 AEANEIDA OR SPIDERS. 



of spinning webs, in which their prey is trapped. Spiders have 

 either two, six, or eight eyes or ocelli (fig. 47, b, /), which vary 

 in position and size, and which supply important characters of 

 systematic value. The jaws with which the spider seizes its 

 prey are inserted immediately under the anterior margin of the 

 cephalothorax, and have, as a rule, on the extremity of their 

 inner surface a groove, with sharp teeth at the sides, into which 

 fits the fang when in a state of repose (b, n, and c, vi). The 

 fang or last joint of the so-called " falsis " is perforated by a 

 minute hole at the tip, through which a colourless poisonous 

 liquid exudes, secreted by the poison-glands within. 



Perhaps the most important structural feature to notice in 

 the spider is the presence of the so-called " spinnerets." These 

 structures are placed at the end of the body, and consist of two, 

 three, or four pairs of appendages. The spinnerets ^■ary in 

 form : some are cylindrical, others round, and some conical. 

 The tip and under-side of these structures are perforated with 

 minute holes. Through these minute apertures the liquid sub- 

 stance that will harden and form the silk of the web is passed. 

 Thus it will be seen that numbers of minute threads of this 

 glue-like liquid are passed out, and these unite into one firm yet 

 elastic line of extreme fineness, but nevertheless of sufficient 

 strength to bear a heavy-bodied spider. This line is also covered 

 with little drops of a clear liquid (fig. 48, c), so that the spider's 

 web consists of two substances — one forming the solid elastic 

 thread, the other forming the little globules. There is a popular 

 idea that the spider can withdraw its web into its body again : 

 this is not correct. When once hardened, the web always 

 remains so. In the spider's web, the viscid globular glue on the 

 web is distributed only over certain areas : passages are left, so 

 that the spider can walk along the web without coming in 

 contact with the sticky substance. This substance is for catch- 

 ing and retaining the insects that fly into the web. In some 

 spiders this webbing is formed for talking aerial flights. The so- 

 called " gossamer '' web is formed by strands of fine silk blowing 



