21 



be damaged in the process ou account of its intimate 

 connection, by means of fibres, with the body wall. 



The buccal mass, as seen in dorsal view (fig. 12), is 

 roughly rectangular in outline with the broad sides 

 lateral. The anterior quarter of the rectangle contains 

 the buccal cavity and the remainder constitutes the 

 broadened anterior end of the radular sac, the rest of 

 which will be seen later. The gullet is a thin-walled 

 tube which opens at the junction of these two regions, 

 and then runs backwards covering and concealing from 

 view the radular sac. The four buccal ducts (fig. IG) are 

 seen running forwards with a somewhat wavy course, the 

 two outer lie freely at the sides of the gullet, the inner 

 run above the dorsal wall of the gullet to which they are 

 closely attached. All four ducts open at about the level 

 of the beginning of the gullet by piercing two thickened 

 dorso-lateral areas, which will be discussed later on in con- 

 nection with the glands. The gut cavity is wider at this 

 level than further back, and these thickenings have been 

 homologised with the dorso-lateral buccal pouches of 

 Haliotis. 



The Buccal Cavity is best studied by comparing the 

 results of median dorsal incision, lateral incision, 

 longitudinal median section, and transverse section in a 

 few specimens (figs. 6 and 12). The following points are 

 to be noted : — 



[a) The situation of the cavity. — As the mouth is 

 ventral, the morphologically front and back ends of the 

 cavity are topographically ventral and dorsal, while the 

 morphological roof and floor are respectively anterior 

 and posterior. In describing the cavity we shall refer to 

 the jDarts in their morphological relations. The main or 

 palatal buccal cavity has a posterior extension, which we 

 shall call the post-palatal buccal cavity, situated on the 



