ANATOMY AND DEVELOPMENT OP PBRIPATUS OAPBNSIS. 225 



cells lining the ducts of the salivary glands pass, without 

 any sharp line of demarcation, into those of the oral epi- 

 thelium, which are flatter and have their nuclei placed in the 

 middle. 



The Pharynx.— The pharynx is a highly muscular tube (fig. 

 7) with a triangular lumen (figs. 14, 15), which extends from 

 the mouth to about half way between the first and second pair 

 of legs. It is lined by a flattish epithelium bounded by a cuticle 

 continuous with that of the mouth. On the dorsal side is a 

 ridge projecting into the lumen of the pharynx. This ridge 

 may be traced forwards (PI. XVI, figs. 11 — 14) into the 

 tongue, and the two grooves at the side of this ridge, forming 

 the two upper angles of the triangular lumen, may be followed 

 into those at the sides of the tongue. The muscles of the 

 pharynx are very highly developed, consisting of an intrinsic 

 and an extrinsic set. The former consists, as is best seen in 

 longitudinal sections, of (PL XVIII, fig. 23) radial fibres, 

 arranged in somewhat wedge-shaped laminse, between which 

 are rings of circular fibres. The latter are thicker externally 

 than internally, and so also appear wedge-shaped in longitu- 

 dinal sections. Very characteristic of the pharynx are the two 

 sympathetic nerves placed close to the two dorsal angles of 

 the triangular lumen (fig. 14, «y). 



The pharynx of Peripatus is interesting in that it is unlike, 

 so far as I know, the pharynx of any true Arthropod, in all of 

 which the region corresponding with the pharynx of Peripatus 

 is provided with relatively very thin walls. 



The pharynx of Peripatus has, on the other hand, a very 

 close and obvious resemblance to that of many of the Chaetopoda, 

 a resemblance which is greatly increased by the characteristic 

 course of the sympathetic nerves. 



The form of the lumen, as already pointed out by Grube, 

 resembles that of the Nematoda. 



The (Esophagus. — Behind the pharynx there follows a narrow 

 oesophagus (fig. 7, o e) shown in section in fig. 16. It has 

 somewhat folded and fairly thick walls, and lies freely in the 

 central division of the body cavity without any mesenteric 



