VI 



PROTRACHEATA , 



429 



It falls into the following divisions : buccal cavity, pharynx, oeso- 

 phagus, mid-gut or stomach-intestine, and rectum. The buecal cavity, 

 in whose base the mouth proper lies, .arises ontogenetically by the 

 growing together of a row of papillae surrounding the mouth ; the 

 mouth and jaws are thus enclosed within a circular wall. In front 

 of the mouth, within the buccal cavity, lies a median prominence, the 

 tongue. At the back of the buccal cavity, where it passes into the 

 pharynx, i.e. at the posterior edge of the 

 mouth, is an invagination directed back- 

 wards, into which the unpaired terminal 

 portion of two salivary glands enters ; 

 these glands are long tubes running 

 through the greater part of the body 

 longitudinally in the lateral divisions of 

 the body cavity. At the anterior end, 

 near the bend towards the common ter- 

 minal division, each salivary gland has 

 a ccecal vesicular appendage. The 

 pharynx, which reaches to the region 

 between the first and second pair of 

 legs, possesses a very thick muscular 

 wall : its lumen in a transverse section 

 is Y-shaped. The oesophagus is shorter. 

 Its wall, which consists of an outer 

 longitudinal and an inner circular mus- 

 cular layer, is much thinner than that of of Peripatus capensis, ventral side, laid 



open (after Balfour). a, Antenna; z, 

 tongue ; fc, jaw ; dg, salivary gland ; gs, 



3 s 



FIG. 292. Anterior end of the body 



are 



common terminal portion of the two 

 salivary glands ; ph, pharynx ; ce, oaso- 

 phagus ; I, the lip papillae surrounding 

 the buccal cavity ; op, oral or slime 

 papillge ; sld, duct or reservoir of the 

 slime glands. 



the pharynx. These three divisions 

 lined by the chitinous cuticle. 



The stomach - intestine stretches 

 from near the two pairs of legs almost 

 to the end of the body. Its wall is in 

 folds, and its muscular layer (outer cir- 

 cular and inner longitudinal, i.e. the reverse of what obtains in all 

 anterior sections of the canal) is exceedingly thin. It is nowhere 

 fastened to the body wall by mesenteries. The rectum, which is 

 distinctly separated from the mid-gut, is considerably narrower, with 

 a tolerably well-developed muscular wall. 



An endothelium (peritoneal epithelium) covers the outer muscular 

 wall of the enteric canal and the other organs lying in or forming the 

 boundary of the body cavity. 



The nervous system of Peripatus (Fig. 293) consists of a large 

 brain placed in the head in front of and over the pharynx (supra- 

 oesophageal ganglion), and of two ventral longitudinal nerve trunks 

 proceeding from the brain, which run far apart in the lateral divisions 

 of the body cavity to its posterior end. In each segment, i.e. in each 

 part of the body corresponding with a pair of extremities, the longi- 

 tudinal nerves are connected by several transverse commissures (9 -10 in 



