586 Transactions. 



Alimentary System. Plate XXVIII, fig. 6 ; Plate XXIX, fig. .3. 



The mouth perforates the thick muscular wall of the ventral side of the 

 head in a direction vertically upwards, and leads into the cavity of the 

 buccal mass — the " buccal cavity." The buccal mass is situated in the 

 head, the cavity of which it practically fills. It is spherical in shape, of a 

 dark colour, and is very muscular. Lying on the dorsal surface of the buccal 

 mass, and usually almost concealing it, is a pair of salivary glands, one on 

 each side. The oesophagus passes away from the buccal mass on the dorsal 

 surface, arising near the anterior end, and, following the curve of the buccal 

 mass, it passes backwards and downwards till it reaches the floor of the 

 body-cavity, where it soon enters the stomach, which it joins on the ventral 

 region of the anterior surface, the transition from oesophagus to stomach 

 being very marked (Plate XXIX, fig. 3 ; oe, st). The stomach extends 

 from the buccal mass to the posterior end of the creature, occupying a large 

 part of the left half of the body-cavity. When distended it is cyhndrical^ 

 and is of smaller diameter in the middle than at the two ends (Plate XXVIII, 

 fig. 6; st). The digestive gland is very extensive ; it occupies a large part 

 of the posterior half of the body-cavity, aiid its lobes completely surround 

 the posterior half of the stomach. It is really divisible into a right and a 

 left part ; the left is the larger, and the digestive juice is collected from its 

 various lobes by ductules into the main ducts, which enter the stomach 

 close together on the left side near the posterior end. The right part is 

 much smaller ; its duct joins the stomach on the right side, also near the 

 posterior end (Plate XXVIII, fig. 6 ; dg, dr/). 



The intestine passes away from the left side of the stomach, at the hinder 

 end, posterior to and below the ducts of the digestive gland (Plate XXVIII, 

 fig. 6; i). It is at first wide, but soon becomes a narrow thick-walled tube. 

 After passing forwards and upwards it coils twice among the lobes of the 

 digestive gland, and comes on to the dorsal surface on the right side, near the 

 posterior end of the creature. It then runs forwards as the thin wall rectum, 

 which on reaching about the middle of the length of the animal takes a sharp 

 turn to the right, ending at the anus on the lower side of the respiratory orifice. 

 Just inside the mouth, at the entrance to the cavity of the buccal mass,^ 

 there is a chitinous jaw. This jaw is crescentic in outline, and extends from 

 side to side of the buccal cavity on the anterior side of the mouth. When 

 the creature is fully distended the jaw comes to the surface, and assists in 

 breaking up food. It is attached at the lower end of the thick muscular 

 anterior wall of the buccal mass to the chitinous lining of this region. The 

 structure of this jaw is very similar to that of a radula ; it is composed of 

 a basement membrane of chitinous material, beset with numerous smal 

 teeth. These teeth are cylindrical, pointed, all alike, and very numerous. 



Captain Hutton seems to have incorrectly described this jaw as " An- 

 terior margin papillate — ^rest smooth."* 



The epithelium lining the buccal cavity is everywhere covered by a layer 

 of chitin, which varies in thickness. 



This cavity is blocked up by two similar and symmetrical muscular 

 masses, one on each side of the middle line. Each is simply a muscular 

 thickening of the wall of its respective side. Also projecting into the 

 buccal cavity, behind these structures just described, is the " odontophore," 

 with the radula. The radular teeth are comparatively small, very numerous, 

 as in Helix, and are carried on a chitinous basal membrane. They are 



* Trans. N.Z. Inst., vol. 15, p. 141. 



