LAND SNAILS. 



15 



the border of tlie aperture lias a thickened white rim, or lip, 

 as it is called. Such a collection having been made, the 

 pupil will find among them some of the following kinds : 



FIG. 17. THE SHELLS OF LAND SNAILS. 



14. The snail, as it crawls along, leaves a slimy trail af- 

 ter it. This trail consists of a fluid, which not only flows 

 from the creeping disk, but also from the surface of the 

 body. If the back of the snail is irritated by a sharp- 

 pointed stick, a little whitish mass of this fluid, or mucus, 

 will adhere to the end of the stick. 



By placing the snail on a piece of glass, and allowing it 

 to adhere and crawl on it, a good view may be obtained of 

 the peculiar movements of this creeping disk, by looking 

 through the glass from the other side. 



The breathing-orifice may be found just within the aper- 

 ture of the shell, on the right side of the snail. 



This orifice will be seen opening and closing at intervals. 

 (See Fig. 18, I.) 



15. In the fresh-water snails there are but two tentacles 

 upon the head. In the land snails with few exceptions, the 



