402 THE OCEAN WORLD. 



distinct, especially in the upper part, but the organs with which it 

 is provided are prominent. These organs are in reality tentacles, 

 although they are more popularly known as horns, especially among 

 children those charming ignoramuses who have been taught to 

 repeat the well-known stanza 



" Snail, snail, come out of your hole, 

 Or else I'll beat you black as a coal " 



which finds its counterpart in all European languages. There are 

 two pair of these tentacles or horns ; one pair quite in front and 

 above, and another smaller and less forward. The first are distin- 

 guished by their size, and also by a black spot or point at their 

 extremity, which is sometimes erroneously said to be the eye of the 

 snail. 



These tentacles differ in many respects from the same organs in 

 other molluscs; they are retractile, and can be drawn altogether 

 within the animal into a sort of sheath, by the contraction of a muscle. 

 At the anterior extremity of the head we find a sort of plaited opening, 

 which is the mouth : it is of moderate extent, closed in front by two 

 lips, and armed with two shear-like organs of horny consistence, one 

 of them being a sort of rasp, which occupies the plate of the buccal 

 cavity, and may be called a tongue ; the other is a median jaw, 

 placed transversely in the membranous walls of the palate, terminating 

 in a free edge, armed with small teeth. This cutting blade, however, 

 executes no movement ; but the lingual organ, pressing all alimentary 

 matter forcibly against its lower edge, effects their mastication, and 

 enables it to dispose of fruit, tender leaves, mushrooms, and other 

 substances easily divided. 



At the bottom of the mouth is an oesophagus, or gullet, to which 

 succeeds a stomach of moderate size. The intestine lies in folds round 

 the liver, which is divided into four lobes, and terminates in a special 

 orifice. 



The little lung of the snail is placed in a cavity, vast for its size, 

 just above the general mass of the viscera, and occupies all the last 

 spiral turn of the cavity. 



The mechanism of respiration is as follows : The animal inhales the 

 air into its lung by forcibly dilating the pulmonary orifice, which lies 



