bigklow] STUDY OF LAND-SNAIL 203 



Now observe the manner in which the feelers are put out and drawn 

 in. The tip is always the last to come out and the first to be drawn 

 in. The process of withdrawing the feelers can be illustrated by 

 fastening threads to the tip of a glove-finger both inside and outside 

 and then pulling on the strings to cause withdrawal and protrusion. 



Observe how the snail makes use of its feelers in moving from place 

 to place and in detecting the presence of food. Bring a pencil near 

 the feeler and notice if the snail responds. Does the animal seem to 

 see ? Also how does it respond when the feeler is touched lightly ? 

 What good are the feelers to the snail ? Do they assist the snail in 

 taking care of itself ? Note the transparency of the feelers (sometimes 

 the eye can be followed even to the base of the feeler as it is being 

 inverted. 



Find the mouth (this can be seen very well if the glass is turned 

 over; the snail will not fall off). There are two side lips and one 

 small lower lip. When feeding so that the mouth is open, the 

 crescentic row of little brownish, comb-like teeth can be seen. The 

 floor of the mouth is covered with rows of tiny little teeth. 



Watch the snail eat. Examine a little of the partly eaten lettuce 

 which shows the teeth marks. Listen while the animal eats and you 

 will hear a rasping sound. 



The broad expanded fleshy portion which adheres so firmly to the 

 glass is the foot. Watch the foot from the under side while the 

 animal is crawling over the glass, and see the waves which are 

 passing over the foot. The motion is the result of a series of con- 

 tractions in the muscles of the foot. Watch the animal crawling about 

 in various positions and note how the shell is carried. 



How much of the animal comes out of the shell? (The head and 

 foot are the only parts that ever protrude from the shell. A museum 

 specimen with shell partly removed will show just what part is always 

 within the shell. In such a museum specimen, notice that the 

 parts which can be protruded are leathery, while the parts protected 

 by the shell are covered with a skin so thin that all the inside of the 

 snail can be easily seen through). 



Feel the skin, note that it is soft and moist with a slime. Trails 

 of this slime can be seen on the glass plates. A similar slime together 

 with some lime which the animal gets from its food are the materials 

 which make the shell. The slime hardens quickly and can often be 

 seen, forming a covering to the snail when at rest or when the atmos- 

 phere of its vivarium becomes too dry. 



