328 



PHYTIVOROUS MOLLUSCA. 



(Fig. 63, 5, a), from the Common Limpet : it is a narrow ri- 

 band-like body, fully three inches long, of nearly equal breadth 

 throughout, except at the apex, where it is soft and some- 



Fig. 63, 5, a, the tongue, natural size, of the Common Limpet (Patella vulgata); 6, a 

 portion magnified ; c, c, c, the cartilaginous jaws. Fig. 6, jaws of Tritonia. 



what dilated, the surface roughened with three rows of teeth, 

 the side rows alternating with the middle one, which is qua- 

 drifid, while the side teeth are divided only into two points. 

 This curious spinigerous tongue is never protruded beyond 

 the margin of the lips. It seems to be used for rasping- 

 down the food ; and, in proportion as the anterior prickles 

 are worn away in this operation and absorbed, another por- 

 tion of the tongue is brought forward to supply its place ; 

 but, that there may be no deficiency in its length, we find 

 the apex soft and vascular, where, in fact, a continual 

 growth and addition are going on.* 



When a phytophagous Gasteropod is about to eat, it 

 thrusts forward, and to a certain extent evolves, the spinous 

 tongue, protruding at the same time the lip on each side, 

 by which the tongue is compressed and forced into the 

 form of the bowl of a spoon. The food is now taken hold 

 on by the lips, drawn forwards and retained by the prickly 

 tongue, and simultaneously pressed against the upper horny 

 jaw, by which means a portion is bitten off, sometimes with 

 a very audible noise. The detached morsel is then passed 

 along the tongue, torn and rasped down by its sharp prickle's, 

 and, forced on by the peristaltic motion of the organ, and 

 by the retropulsive action of the adjacent muscles, the mass 

 is made to enter the gullet. At the entrance of this canal 

 there is an uvular caruncle, which is probably the seat of 



* Cuv. Mem. sur la Patelle, p. 18. 



