SECT. XI. 



TONGUES OF MOLLUSC A. 



23: 



Fig. 170. The tongue of Helix aspersa. 



behind, but in front it is spread into a nearly flat narrow 

 plate, traversed by numerous rows of minute recurved 

 teeth, or spines set 

 upon flattened plates ; 

 in the Garden Snail 

 or Slug each principal 

 tooth has its own 

 plate. Tig. 170 re- 

 presents a magnified 

 portion of a Snail's 

 tongue by Dr. Car- 

 penter ; the rows at 

 the edge are sepa- 

 rated to show the 



structure. The teeth are set close one to another, 

 and are often very numerous. In the Helix pomatia, 

 a snail found in the middle and southern counties of 

 England, they amount to 21,000, and in the great 

 slug (Arion ater), there are 26,800. This kind of 

 tongue only serves for 

 rasping vegetable food. 

 All the Trochidse, which 

 are marine mollusksthat 

 are supposed by some 

 naturalists to live on 

 fuci, are remarkable for 

 the length and beauty 

 of their narrow spiny 

 tongues. Fig. 171 is a 

 small portion of the 

 tongue or palate of the 

 Trochus zizyphinus, 

 highly magnified ; the 

 large teeth of the lateral 

 bands, as well as the small teeth in the centre, have 

 minutely serrated edges. Fig. 172 shows the Trochus 

 granulatus in the act of crawling. 



Fig. 171. Palate of Trochus zizyphinus. 



