112 



ZOOLOGY. 



Americanus, found under logs, etc. The centipede (Scolo- 

 pendra heros) is very poisonous, the poison-sacs being 

 lodged in the two large fangs or second pair of jaw-legs. 



Fig. 133.— Julus. 



Fig 134.— Geophilus. 

 .Natural size. 



Class V. — Arachnida. 



General Characters of Arachnids. — The bodies of spiders 

 and scorpions, etc., are divided into two regions, a head- 

 thorax and abdomen, the head being closely united with 

 the thorax. There are no antennae, only a pair of mandi- 

 bles and a pair of maxilla?, with four pairs of legs. There 

 are never any compound eyes. The young are usually like 

 the adult, except in the mites, in which there is a slight 

 metamorphosis, the young being born with but three pairs 

 of legs, while the full-grown mite has four pairs. 



An example of the sub-class is the spider, which is char- 

 acterized by having two or three pairs of spinnerets, out 

 of which the silk is drawn in spinning their webs. Besides 

 breathing by air-tubes, spiders have so-called lungs com- 

 posed of several leaves, into which the blood flows, 



