24 CLASS ARACHNIDA 



Order ARANEIDA. 



This group includes tlie familiar spiders which are very 

 generally distributed over the world, and occupy a rather 

 conspicuous ])lace among other animals. Their body is 

 sharply dixided into cephalothorax and abdomen, and the 

 four j)airs of legs nrv usually nearly ec|ual in length. The 



Fig. 3. — Epeira scohpeturia, showing iiornuil position of spider in web 

 head downward. A vibrator at .t agitating the web will cause the spider 

 to rush at once to point of contact. (Photo by Prof. W. M. Barrows.) 



eyes are sim])le and usually eight in numl)er, and the large 

 mandibles are attached at right angles to the axis of the 

 body. In some species these are provided with a poison 

 duct. The bite is venomous to smaller organisms, and in 

 some of the larger, like the tarantula, the bite is a serious 

 matter for man. Sj^iders offer a great many attractive 



