SPIDERS /tND THEIR IVEB-MAKING 



193 



any antennae? The eyes of spiders are simple (not com- 

 pound as in the insects and crustaceans), and they vary 

 in number and size and arrangement in the different 

 kinds. Find the mandibles or jaws; with a pin press 

 them apart and examine them. How do they work'' 

 Note that each jaw (fig. 150) is composed of a firm, 

 smooth, sharp-pointed tip called the fang, and a thicker 

 hairy basal part, the falx. In the falx is the tiny poison- 

 sac, from which the poison runs through the fang and out 

 through a hole near the point. All 

 spiders have poison-sacs, but with 

 only a few of the larger ones is enough 

 poison introduced into the wound to 

 make a bite at all painful to us. 



Examine now the spinning-organs. 

 At the posterior tip of the abdomen 

 may be seen a few small finger-like 

 projections, the spinnerets (fig. 151). 

 Each of these movable spinnerets 

 bears on its surface many very small 

 papilla;, the spinning-tubes (fig. 151). 

 These can be seen by examining a 

 spinneret under the microscope. In 

 spinning, a slender silken thread 

 issues from each of the spinning-tubes 

 on each spinneret. All of these fine 

 threads unite to form one strong line 

 which we see. 



The hunting-spiders. — Some kinds of spiders spin 

 webs for catching their prey, while some do not, but 

 trust to pursuit by running and leaping. The house- 

 spiders with their cobwebs, the field-spiders with their 

 silken sheets among the grasses, and garden-spiders with 

 their geometrically regular orbs hung in the shrubbery, 

 belong to the web-weaving group. The black, swift 



Fig. 151. — The six spin- 

 nerets enlarged (bel(jw) 

 of a spider, witli 

 one spinneret magni- 

 fied (above) to show 

 the spinning "spools" 

 or tubes. {From Jenkins 

 and Kellogg.) 



