112 INVERTEBRATE ZOOLOGY 



GASTROPODA 



A PULMONATE GASTROPOD. A LAND SNAIL {Helix pomatia) 



This snail 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 Philadelphia. 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 disc of 

 calcined slime called the epiphragma. If it is still in winter 

 quarters, when obtained, the epiphragma should be removed 

 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 

 expanded in from one to two days. If the air be 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 

 unsegmented 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 



