10 WALTER K. FISnER, 



like depression leading out onto the "lower" lip. It is lined with thick 

 cuticle, secreted by a cylindrical epithelium. At either side the epi- 

 thelium rests on a core of supporting cells resembling those which 

 make up the buccal cartilages. This sublingual groove acts as a 

 track on which the sublingual organ slides out and back, with the 

 working of the odontophore, and the cuticle is probably a protection 

 against the teeth of the sublingual organ. 



The lateral pouches of the oral cavity are merely pockets on 

 either side of the odontophore, between it and the palps. 



Just above and almost in communication with the palps, on either 

 dorso-lateral wall of the oral cavity begins a thick fold {Bf Figs. 2, 

 4, 9). These two presently become the dorsal or greater folds of 

 pharynx and oesophagus. From their commencement just above the 

 palps, to about the beginning of the pharyngeal or posterior buccal 

 gland, the folds are filled with mucous cells of large size, which open 

 into the oral cavity, or pharynx, as they are forwardly or posteriorly 

 situated. Each cell (ilf. C Fig. 25) consists of a long tube leading 

 from the epithelium through the connective and muscular tissue, to 

 the base of the fold where it ends in a vacuolated expansion, the cell 

 proper. This stains deeply with haematoxylin. It is probable that 

 the cells secrete mucus which may serve to entangle bits of food 

 into a sort of string. In fresh specimens, yet alive, these folds are 

 seen to be covered with a transparent glairy secretion and are of a 

 pale yellowish color. The epithelium of the folds or ridges is colum- 

 nar and ciliated, the cells being higher than those forming the remainder 

 of the lining of the posterior portion of the buccal cavity. 



The oral cavity passes into the dilated pharynx or crop. The 

 opening of the radula tube is covered by a prominent lip. There are 

 regular constrictions in the pharynx which form rather deep lateral 

 pockets, but the mid-dorsal and mid-ventral regions are occupied re- 

 spectively by the dorsal or greater and ventral or lesser folds of the 

 pharynx and oesophagus. The former begin, as mentioned above, in 

 two dorso-lateral ridges of the oral cavity. These rapidly approach 

 each other (Fig. 2) and come to occupy the mid-dorsal line, with the 

 beginning of the pharynx. At the posterior end of the pharynx they 

 pass to the left, around the oesophagus {Df Fig. 6), come to lie on 

 the ventral side, and finally reach the right side, where they end 

 abruptly with the proventriculus or fore chamber of the stomach {Pro). 

 The two folds are so deep that the free edges are folded back, as 

 they hang in the narrow lumen of the oesophagus. Smaller, length- 



