Myriapoda. 55 



nized by their habit of coiling into a spiral when disturbed ; 

 they have two pairs of legs to each segment. They are 

 vegetarian and not poisonous. 



FIG. 39. SKEIN CENTIPED. 



Both of these forms are usually to be found by over- 

 turning stones and logs ; the centipeds seek safety by run- 

 ning briskly away, while the millipeds coil up and lie still. 



CLASS ARACHNIDA. 



The Spiders. The body of a spider consists of two 

 parts, connected by a constricted waist, the unsegmented 

 cephalothorax and ^, large, soft, unsegmented abdomen. 

 There are six pairs of appendages : first, the jaws, each 

 jaw ending in a sharp, incurved segment at whose apex 

 opens the duct of a poison gland ; second, the palps, which 

 are sometimes mistaken for a pair of legs ; and lastly, four 

 pairs of legs. 



Spiders have from one to four pairs of simple eyes vari- 

 ously arranged on the top or front of the head. Spi- 

 ders have a well-developed sense of sight, and their sense 

 of touch is very delicate. Of their other senses little is 

 known. 



