34 



and otlior sppfial featurps are tlio fewness of teeth in each 

 row, aiul the high deg-ree of specialisation of the 

 individual tooth. These characters sharply difteientiate 

 the Docoglossa from other Gastropods, for the specialisa- 

 tion of their ladiila is certainly along- a Hue divcra'ina' 

 absolutely from that adopted hy the Tienioglossa, wheie 

 the fewness of teeth pei- row is due to several having 

 fused to form compound ones. 



To this account of the alimentary canal we may add 

 a short desciiption of the relations of the various parts 

 of the fo]'e-gut to the feeding process. The generalised 

 diagram of a median longitudinal section of Pidilln, given 

 in fig. (i, is intended to illustrate these relations. 



By contraction of its strong ventral ])rotractor muscles 

 the tip of the odontophore is extruded from between the 

 lips, and the radula is rubbed along the rock surface from 

 behind forwards to scrape off minute Algte. The outer 

 lips, aided l)y the " licker," seize and hold any fragments 

 torn from the rock, the dorsal palatal plate greatly 

 strengthening the dorsal outer lij) for this purpose, besides 

 lifting the roof of the buccal cavity out of reach of the 

 rasping radula. The food, consisting of small Algie and 

 tiny org-anisms of various kinds, with an admixture of 

 rock substance, is then passed into the buccal cavitv from 

 which its exit is barred by the closure of the inner lips. 

 The mouth parts are almost always examined when both 

 they and the head are in a retracted condition, and it 

 may be that the oesophageal pouches are, in pait, spaie 

 folds of tissue allowing the protrusion of the odontophore 

 without breakage of any of the gut lining. Specimens 

 paralysed by a dilute solution of chloral hydrate in sea 

 water often die with the head partly ex])anded, and they 

 certainly seem to show less folding in the region of the 

 cesoph ageal pouches. 



