226 TRANSACTIONS LIVEKPOOL BIOLOGICAL SOCIETY. 



and other special features are the fewness of teeth in each 

 row, and the high degree of specialisation of the 

 individual tooth. These characters sharply differentiate 

 the Docoglossa from other Gastropods, for the specialisa- 

 tion of their radula is certainly along a line diverging 

 absolutely from that adopted by the Tsenioglossa, where 

 the fewness of teeth per row is due to several having 

 fused to form compound ones. 



To this account of the alimentary canal we ma}' add 

 a short description of the relations of the various parts 

 of the fore-gut to the feeding process. The generalised 

 diagram of a median longitudinal section of Patella, given 

 in fig. 6, is intended to illustrate these relations. 



By contraction of its strong ventral protractor 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 Algse. The outer 

 lips, aided by the " licker," seize and hold any fragments 

 torn from the rock, the dorsal palatal plate greatly 

 strengthening the dorsal outer lip for this purpose, besides 

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

 rasping radula. The food, consisting of small Alga? and 

 tiny organisms of various kinds, with an admixture of 

 rock substance, is then passed into the buccal cavity 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 part, spare 

 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 expanded, and they 

 certainly seem to show less folding in the region of the 

 oesophageal pouches, 



