2 FIRST BOOK OF ZOOLOGY. 



2. Remember that the shell is not a house built by the 

 snail, as a wasp builds its nest, but the shell is a part of the 

 animal, and is connected to it by certain muscles, so that it 

 cannot leave the shell, as many suppose. 



The empty, or dead, shells, are to be studied first. 



Looking over the shells collected, we shall find some of 

 the following kinds : 



FIG. 1. FRESH-WATEB SHELLS. 



A number of fresh-water mussel-shells, also, will prob- 

 ably be collected. 



FIG. 2. FRESH- WATEK MUSSEL-SHELL. 



These are to be reserved for future examination. Those 



