112 ZOOLOGY, 
Americamis, found under logs, etc. The centipede (Scolo- 
pendra lieros) is Tery poisonous, the poison-sacs being 
lodged in the two large fangs or second pair of jaw-legs. 
Fig. 133.— Julus. Fig. lU.^Geophilus. 
Natural size. 
Class V. — Arachnida. 
General Characters of Arachnids. — The bodies of spiders 
and scorpions, etc., are diyided 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 maxillae, 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, si)iders have so-called lungs com- 
posed of several leaves, into which the blood flow§. 
