8/8 ANATOMY AND DEVELOPMENT 



PART II. 



ALIMENTARY CANAL. 



The alimentary canal of Peripatns capcnsis forms, in the 

 extended condition of the animal, a nearly straight tube, slightly 

 longer than the body, the general characters of which are shewn 

 in figs. 6 and 7. 



For the purposes of description, it may conveniently be di- 

 vided into five regions, viz. (i) the buccal cavity with the tongue, 

 jaws, and salivary glands, (2) pharynx, (3) the oesophagus, (4) 

 the stomach, (5) the rectum. 



The Buccal Cavity. The buccal cavity has the form of a 

 fairly deep pit, of a longitudinal oval form, placed on the ventral 

 surface of the head, and surrounded by a tumid lip. 



[The buccal cavity has been shewn by Moseley to be formed 

 in the embryo by the fusion of a series of processes surrounding 

 the true mouth-opening, and enclosing in their fusion the jaws.] 



The lip is covered by a soft skin, in which are numerous 

 organs of touch, similar to those in other parts of the skin having 

 their projecting portions enclosed in delicate spines formed by 

 the cuticle. The skin of the lips differs, however, from the re- 

 mainder of the skin, in the absence of tubercles, and in the great 

 reduction of the thickness of the dermis. It is raised into a 

 series of papilliform ridges, whose general form is shewn in fig. 5; 

 of these there is one unpaired and median behind, and a pair, 

 differing somewhat in character from the remainder, in front, and 

 there are, in addition, seven on each side. 



The structures within the buccal cavity are shewn as they 

 appear in surface views in figs. 5 and 7, but their real nature is 

 best seen in sections, and is illustrated by PI. 49, figs. II and 12, 

 representing the oral cavity in transverse section, and by PI. 49, 

 figs. 17 and 1 8, representing it in horizontal longitudinal sections. 

 In the median line of the buccal cavity in .front is placed a thick 

 muscular protuberance, which may perhaps conveniently be 

 called the tongue, though attached to the dorsal instead of 

 the ventral wall of the mouth. It has the form of an elongated 



