A LAND SNAIL 93 



Class : Gastropoda. Order : Pulmonata 

 A LAND SNAIL 



The edible French snail (Helix pomatia) is very common in 

 Europe, in many parts of which it is used for food. It is imported 

 into this country for the same purpose and may be obtained at 

 small cost in New York and other cities. It is especially adapted 

 for dissection, but any large Helix may be used instead. The large 

 slug (Limax maxima) is very similar to Helix in structure and 

 may also be used, but as it has no coiled shell, that feature of the 

 dissection would be omitted. 



The snail is a terrestrial animal and feeds principally upon 

 leaves. It hibernates in the winter under stones and logs, after 

 having first closed the mouth of its shell with a thin disk of 

 hardened, calcified slime called the epiphragma. If it is still in 

 winter quarters when obtained, the epiphragma should be re- 

 moved and the animal placed among fresh leaves in a warm room, 

 when it will soon come out of its shell and begin to feed. Snails 

 are best killed for dissection by drowning. They should be placed 

 in a large, covered jar of water, when they will die extended in 

 from one to two days. If the air is first boiled out of the water, 

 the process will be accelerated, but the animal should not be 

 placed in water which is still hot. 



Study the external characters of the animal. Its body is un- 

 segmented and is covered with a shell, but unlike the shell of the 

 pelecypod that of the snail is a univalve. As in other mollusks, 

 the shell is the cuticula of the animal charged with calcareous 

 salts, and forms an exoskeleton. In shape the shell is an elongated 

 cone which has been twisted to the right, forming a closely coiled 

 spiral. The tip of the spiral is called the apex, the opening is 

 called the mouth, and its axis, the columella. How many turns 

 does the spiral make? The apex corresponds to the umbo of 

 the pelecypod; it is the oldest portion of the shell, the point 

 from which its growth has proceeded. Note the parallel lines 

 of growth. The ventral edge, or mouth, of the shell is thus its 

 youngest part. The animal can withdraw its entire body within 



