BUCCINUM. 283 



pharynx, which bears no teeth, projects the tongue 

 apparatus, and the muscles of this characteristic organ 

 almost surround the anterior part Of the alimentary 

 canal. The whole structure is known as the Odontophore 

 (Text-fig. 4, Od.), and consists essentially of a tongue, 

 projecting into the pharyngeal space, covered by a 

 flexible rasp — a membrane set with teeth — known as the 

 radula. A description of this apparatus is given 

 separately below. 



The pharynx extends backwards for about 1 cm., and 

 almost at the point where the radular apparatus opens into 

 it, two salivary ducts enter laterally, one on either side 

 (PI. II, fig. 12, Sal. d.). These ducts can be seen as two 

 delicate white tubes running along the sides of the 

 oesophagus (fig. 12, Oes.), the next portion of the gut. 



The Oesophagus extends from the pharynx to the 

 stomach, and is the longest section of the alimentary 

 canal. The most distal part, immediately behind the 

 pharynx, is flattened dorsoventrally and runs along 

 through the proboscis to its posterior end. Here it turns 

 abruptly on itself and runs forward again in close contact 

 with the proboscis sheath. The anterior direction is kept 

 until the region is reached where the nerve collar lies 

 hidden by the conspicuous salivary glands, and then 

 another somewhat abrupt bend occurs (Text-fig. 4, a and b) 

 and the oesophagus passes through the nerve ring and 

 runs posteriorly along the floor of the body cavity. This 

 curious looping of the oesophagus is probably due to the 

 nerve collar which has retained its normal anterior 

 position and compelled the alimentary canal to take the 

 course which has been described. The part of the gut 

 which is thus bent into an S is marked by longitudinal 

 folds projecting into the lumen. None of these 

 longitudinal folds arc specialised or better developed 



