Fig. 159. SECTION OF WALL 

 OF SUCKING STOMACH 



The Internal Anatomy of Spiders 



The fore-intestine is that portion of the alimentary canal 

 that is developed from an infolding of the ectoderm at the anterior 

 end of the embryo, the stomodceum. It consists of the pharynx, 

 the oesophagus, and the sucking stomach. 



The histological structure of the fore-intestine is the same 

 as that of the body-wall; the lumen being lined with a chitinous 

 intima, a continuation of the cuticula; and, surrounding this, 

 there is an epithelial layer, continuous 

 with the hypodermis; and this in turn 

 is bounded on the side toward the 

 body-cavity by a basement mem- 

 brane. The muscular coat of the 

 fore-intestine, which is well-marked 

 in some arachnids, is absent in the 

 true spiders. Figure 1 59 represents a 

 small portion of the wall of the 

 sucking stomach, in this the layers are 

 shown and also the attachment of 

 some muscles. 



The pharynx. — The pharynx or mouth-cavity is situated 

 between the rostrum and the sternum. It extends in a more or 

 less nearly vertical direction (Fig. 143). It is bounded in front 



by a plate borne by the rostrum, which 

 may be termed, by an analogy drawn from 

 the anatomy of insects, the epipharynx; and 

 is bounded behind by a plate borne by the 

 sternum, which by a similar analogy may 

 be termed the hypopharynx. 



By bringing together the lateral margins 



of the epipharynx and the hypopharynx, a 



tube-like cavity is formed into which the 



spider sucks the juices pressed from its prey 



by the mouth-parts, the tufts of hairs borne 



by the mouth-parts preventing the escape 



of the liquid food. 



The epipharynx is marked by many transverse striae (Fig. 



[60) which lead to a longitudinal slit in its middle line, which in 



turn leads to the opening of the oesophagus. Thus if the mOUth- 



Fig. 160. 

 THE EPIPHARYNX 



'53 



