34 STE0CTURE OF THE TONGUE. 



looks like a slender white thread, two inches or 

 more in length, one end of which is attached to 

 the throat, and the other, which is free, you will 

 see coiled in a beautiful spiral within the cavity of 

 the stomach. 



By allowing this tiny thread to stretch itself on a 

 plate of glass, which is easily done by putting a drop 

 of water on it first, which then may be drained off and 

 dried, you will find that it is in in reality an exces- 

 sively delicate ribbon of transparent cartilaginous 

 substance or membrane, on which are set spinous teeth 

 of glassy texture and brilliancy. They are perfectly 

 regular, and arranged in three rows, of which the mid- 

 dle ones are three-pointed, while in each of the outer 

 rows a three-pointed tooth alternates with a larger 

 curved one somewhat boat-like in form. All the teeth 

 project from the surface of the tongue in hooked 

 curves, and all point in the same direction. 



The action of this sort of tongue is that of a rasp, 

 the projecting teeth abrading the surface of the plants 

 on which the animal feeds, just as the lion is said to 

 act with the horny papillse of his tongue on the flesh 

 of his victijn. The general structure is common to 

 all the Gasteropod Mollusca, but the varieties in the 

 mode and pattern of the dentation are almost infinite. 



The little Top, for example, has the teeth set in 

 eleven longitudinal rows, along the central part of the 

 ribbon, while the edges, which are turned over on each 

 side, are formed into oblique combs; — altogether a 

 very elaborate affair. But even this is exceeded by 

 the tongue of the Livid Top (T. ziziphinusf, a larger 

 and handsomer species not rare among the lower 



