44 LESSON IX. 



Teacher. I intend that you shall study the 

 univalve shells first, because they are the most 

 simple, and their distinguishing characters well 

 marked ; but before you can describe these 

 shells, you must be well acquainted with their 

 parts. Here are some univalve shells, examine 

 them carefully ; I will give you the names for 

 the parts, as you discover them. First, tell me 

 which appear to be the principal parts. 



Child. These shells have two principal parts, 

 this which swells out, and this which is tapering* 



Teacher. The swelling part is called the 

 body,* and this which is tapering, the spire. 

 Observe how the spire is produced. 



Child. It seems formed by the rolling round 

 of a part of the shell. f 



Teacher. These parts that roll round are 

 called whorls, from an old Saxon word signify- 

 ing a round. What do you remark in these 

 whorls ? 



Child. That they gradually increase in size. 



Teacher. The largest forming the- body of 

 the shell is called the body whorl, the smallest 

 is called the first whorl. As the whorls succes- 

 sively roll one round another, what difference is 

 there in the circles they describe ? 



Child. They gradually increase in diameter. 



Teacher. It is from this circumstance that 

 the set of whorls is called the spire, a word 

 derived from the Greek root wceif, (speir,) which 



* See plate I. 

 t See Helix Stagnalis. Plate V. Fig. 3, 



