84 



and otiior sjipcial features are tlie fewness of teetli in each 

 row, and the high degree of specialisation of the 

 individual tooth. These characters sharply difterentiate 

 the Docoglossa from other Gastropods, tor the specialisa- 

 tion of their radiila is certainly along a line diverging 

 ahsolutely from that adopted by the Taenioglossa, where 

 ilie fewness of teeth per 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 fore-gut to the feeding pi'ocess. The generalised 

 diagram of a median longitudimxl section of Pafel/a, given 

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



By contraction of its strong ventral protractor mus(des 

 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 oif minute AlgiP. 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 tliis 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 admixtuie of 

 rock substance, is then passed into the buccal cavity from 

 which its exit is barred by the closure of the inner li])s. 

 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, spaie 

 folds of tissiie allowing the ])r()trusion of the odonto])hore 

 without breakage of any of the gut lining. Specimens 

 paralysed by a dilute solution of chloral liydrate in sea 

 water often die with the head partly expanded, and they 

 certainly seem to show less folding in the region of llie 

 (esophageal j)OUches. 



