CHAPTER XIV 



THE SPIDERS AND ALLIES: ARACHNIDA 



A noiseless, patient spider, 



I marked where, on a little promontory, it stood isolated ; 



Marked how, to explore the vacant, vast surrounding, 



It launched forth filament, filament, filament out of itself ; 



Ever unreaching them — ever tirelessly speeding them. 



Walt Whitman 



Spiders. Spiders have several of the anterior somites 

 joined into a single mass, the head-thorax, or cephalothorax 

 (Fig. 74), followed by the abdomen. The cephalothorax 

 bears six pairs of appendages, — two pairs of the nature 

 of jaws and four pairs of walking legs. The chelicerse, the 

 first pair of jaws, are appendages composed of two seg- 

 ments, of which the terminal segment is sharp pointed and 

 hollow, for the passage of a poisonous secretion from a gland 

 placed partly in the head and partly in the basal segment. 

 The second pair of jaws, or pedipalps, bear jointed feelers, 

 used for handling food. On the front of the head are eight 

 simple eyes ; compound eyes and antennae are wanting. 



Two little slits on the under side of the abdomen open into 

 the breathing organs, or lung books, which consist of a pair of 

 sacs containing a number of thin plates, like the leaves of 

 a book. Between the two slits are the external openings 

 of the reproductive organs. At the end of the body are three 

 pairs of spinnerets, consisting of a number of little tubes 

 leading from glands in the abdomen, which secrete a viscous 

 fluid that hardens into silk on exposure to the air. Two 

 tracheae (Fig. 74), which give off branches to different parts 

 of the abdomen, open just in front of the spinnerets. 



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