XX. SPIDERS AND MYRIAPODS 



Structure of the Spider. — Use any large spider for the following work, 

 preferably Argiope, the brightly colored garden spider.* 



Examine the large spider carefully. Notice that it differs from an insect 

 in having the head and thorax joined together to form a cephalothorax. 



Notice the number of legs; 

 here is another difference from 

 insects. Look on the dorsal 

 side of the cephalothorax. 

 The glistening black objects 

 are simple eyes, of which there 

 are usually four pairs. What 

 is the number and position 

 of eyes in this specimen? 

 Make a diagram. Argiope 

 breathes by means of lung- 

 like sacs in the abdomen, the 

 openings of which can some- 

 times be seen just behind the 

 most posterior pair of legs. 

 Another organ possessed by 

 the spider, which insects do 

 not have (except in a larval 

 form), is known as the spin- 

 neret. This is a set of glands 

 which secrete in a liquid state 

 the silk which the spider 

 spins. On exposure to air this fluid hardens and forms a very tough build- 

 ing material which combines lightness with strength. Look carefully at 

 a spider spinning and decide where the spinnerets are located. ^ 



Uses and form of the Web. — The web-making instinct of spiders 

 forms an interesting study. Our common spiders may be grouped accord- 

 ing to the kind of home they build. The web in some cases is used as a 

 home, in others it forms a snare or trap. In some cases the web is used 

 for ballooning, spiders having been noticed clinging to their webs miles 

 out at sea. The webs seen most frequently are the so-called cobwebs. 

 These usually serve as a snare rather than a home, some species remain- 

 ing away from the web. In other cases the spider hangs, back down- 

 ward, under a thin sheet of filmy cross lines. 



The funnel-web makers form a closely woven web which is usually attached 

 to grass or may be found in corners of a building. From one end of the 



* For laboratory work see Hunter and Valentine, Manual, page 117. 



2 Useful laboratory or home work may be given in the form of tabular com- 

 parisons between the various species of "the arthropods. For examples of such 

 tables see Hunter and Valentine, Manual, pages 116, 120, 127, 130. 



256 



Tarantula on its back; p, poison fang; s, spinneret. 

 Reduced from photograph by Davison. 



