ILLINOIS NATURAL HISTORY SURVEY MANUAL 



of the snaiL If a long eye peduncle is touched, the snail immedi- 

 ately withdraws it outside in, in such manner as one sometimes 

 removes the finger of a glove. 



The visible part of the snail's body\ which ends in a slender, 

 tapering tail^ is long and narrow. Irregular granulations that 

 cover the body give it a rough appearance. The underside of 

 the body, known as the/oo/, is flat, and when the snail lifts its 

 head from the log wavelike pulsations along this foot may be 

 seen. Locomotion of the snail is accomplished not by a picking 



YE Peduncle 

 Eye 



Head 



Tentacle 



Fig. 1. — Animal of land snail, Polygyra albolabris (Say). Parts of 

 the body are indicated. 



up and setting down of the foot but by a sliding movement 

 produced by a wave of muscular contractions along the foot. 



The soft part of the animal containing most of the vital 

 organs remains within the shell. It is covered by a tough skin 

 called the mantle. The thickened portion of the mantle which 

 borders the aperture or opening of the shell, and which is known 

 as the mantle collar^ secretes the material which adds new shell 

 around the aperture, for only by the addition of new shell ma- 

 terial around the edge of this opening does the snail shell in- 

 crease in size. 



Noticeable is the mtuus which is exuded from a gland near 

 the mouth. The mucus assists the snail in crawling by smoothing 

 or lubricating the path over which it passes. On the right side 

 of the body, just under the edge of the shell, may be seen the 

 breathing orifice or lung opening through which the snail takes 

 in air, for it is a lung breather just as we are. All of the Illinois 

 land snails are lung breathers, and all species but one belong to 

 the Pulmonata, an order which takes its name from a Latin 

 word meaning lung. 



Let us search the log still farther. We tear off a piece of the 

 bark which is loose or started. On the inner side of this bark we 



