LAND SNAILS. 



15 



the border of the aperture has 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 flows not only 

 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 aperture may be found just within the 

 aperture of the shell, and on the right side in those shells 

 having dextral shells. This orifice will be seen opening and 

 closing at intervals. (See Fig. 18, b.) 



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

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



