;3o 



ARACHNIDA ARANEAE 



At the top of the pharynx, which is nearly perpendicular, the 

 canal continues backwards and upwards as a narrow tube, the 

 oesophagus, passing right through the nerve-mass, which embraces 

 it closely on all sides, to the sucking stomach. At the com- 

 mencement of the oesophagus is the opening of a gland, probably 

 salivary, which is situated in the rostrum. 



We now reach the sucking stomach, which occupies the centre of 

 the cephalothorax. It is placed directly over a skeletal plate, the 

 " endosternite " (Fig- 185, e), to which its lower surface is connected 



by powerful muscles, while its upper 

 wall is protected l;>y a hard plate 

 or " buckler," which is similarly 

 attached to the roof of the cephalo- 

 thorax in the region of the " fovea 

 media." The walls of the stomach 

 are not themselves muscular, but 

 by the contraction of the muscles 

 above mentioned its cavity is en- 

 larged, and fluids from the pharynx 

 are pumped up into it. 



The canal thus far is lined by 

 chitin, like the exterior of the 

 body, and forms a sort of compli- 

 cated mouth-apparatus. 



The Mesenteron lies partly in 

 the cephalothorax and partly in 

 the abdomen. The thoracic portion, 

 shortly behind the sucking stomach, 

 sends forward on either side a large 

 branch or " diverticulum," from each of which five secondary 

 branches or "caeca" are given off (Fig. 185). Of these the 

 anterior pair sometimes join, thus forming a complete ring ; but 

 usually, though adjacent, they remain distinct. The other four 

 pairs of caeca curve downwards, protruding into the coxae of the 

 legs, where they often terminate, but sometimes (Epeira) they con- 

 tinue their curve until they meet, though they never fuse, under the 

 nerve-mass. Behind the origin of the diverticula the mesenteron 

 continues as a widish tube, and shortly passes through the pedicle 

 and enters the abdomen, where, curving slightly upwards, it pro- 

 ceeds along the middle line till it ends in the proctodaeum. 



Fig. 185. — Diagram showing tlie ana- 

 tomy of the cephalotliora.x: of a 

 Spider. The right alimentary cliverti- 

 cnhuu has been removed, a, Aorta ; 

 c, left diverticulnni with secondary 

 caeca ; e, endosternite ; oes, oeso- 

 l")hagus, descending to the mouth ; 

 5, sucking stomach : sh, dorsal 

 shield of sucking stomach. 



