CHAPTER XI 



THE SPIDERS AND ALLIES (ARACHNIDA) AND THE CENTI- 

 PEDS AND MILLEPEDS (MYRIAPODA) 



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.5S, 1), 

 followed by the nearly spherical abdomen (Fig. 58, 2). The 

 cephalothorax bears six pairs of appendages, two pairs 

 of the nature of jaws and four pairs of walking-legs (Fig. 

 58, 3). The mandibles (Fig. 58, 4), the first pair of jaws, are 

 appendages composed of two segments, 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 

 maxillce, bear jointed palpi (Fig. 58, 5), used for handling food. 

 On the front of the head are eight simple eyes ; compound 

 eyes and an ten use are wanting. 



Two little slits on the under side of the abdomen open 

 into the breathing-organs (Fig. 58, 6), which consist of a pair 

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

 a book, through which the blood passes for the exchange 

 of gases. Between the two slits are the external openings 

 of the reproductive organs (Fig. 58, 7). At the end of the 

 body are three pairs of spinnerets (Fig. 58, 0), consisting of 

 a number of little tubes leading from glands in the abdomen, 



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