22 THE SEA -SIDE AND AQUARIUM. 



for rasping down the food ; and in proportion as the 

 anterior prickles are worn away in this operation and 

 absorbed, another portion 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 

 muscular, where in fact a continual growth and ad- 

 dition 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 prickles, 

 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 the animal's taste; and on its 

 side a pair of lobulated salivary glands, or sometimes 

 two pairs, which have each a single excretory duct, 

 to convey their peculiar secretion into its upper part, 

 to lubricate and soften the mass. The gullet is a 

 muscular canal, lined interiorly with a mucous coat, 

 presenting, indeed, the same structure as the whole 



