CHAPTER XI. 



BC0RPI0N8 AND SPIDBB8. 



If we examine a spider we shall see that its body is 

 divided into two regions ; i.e., a head-thorax (cephalotho- 

 rax) ; and hind-body, or abdomen. The head, bearing the 

 simple eyes and jaws, is closely united to the thorax, which 

 bears four pairs of legs. There are no antennae,* but be- 

 hind them the poison-fangs (Fig. 96«, 3); and behind these 

 is a pair of maxillae with palpi (7) which in part supply the 

 place of antennae. The head-thorax of the spider bears 

 usually eight simple eyes, and only two pairs of jointed 

 appendages, while to the thorax are attached four pairs of 

 legs, each ending in two claws. These claws are comb-like 

 beneath (6), and around their bases are stiff hairs, enabling 

 the spider to seize the thread and run with ease over its web. 

 How is the web made ? If we closely examine the under 

 side of the hind-body we may detect the spinnerets (le). 

 There are three pairs of short jointed appendages, with 

 minute 3-jointed tubes (5), out of which passes a clear 

 sticky fluid, which becomes a very fine silken strand when 

 forced out so as to come in contact with the air. Each 

 strand unites to form the thread with which the web is 

 made. Unlike any animals we have yet examined, spiders 

 and their allies breathe by internal air-tubes, the air passing 

 in through openings in the skin called spiracles. In the 

 scorpion four pairs of these spiracles are easily seen ; the 

 spider has but a single pair. Most spiders also have a pair 

 of book-lungs near the base of the hind-body ; in the trap- 

 door spiders there are two pairs. Scorpions chiefly differ 

 from spiders in having the maxillae ending in a forceps, 

 while the long slender jointed hind-body ends in a poison- 

 sting. (See Emerton's Structure and Habits of Spiders, 

 1883.) 



* They have been found to temporarily exist in the embryo. 



