60 LESSON IX 



What is the relative proportion of the parts of 

 the cone ? 



Child. The body whorl is very large, com 

 pared with the other whorls. 



Teacher. This peculiarity is expressed by 

 the term turbinate, which is derived from the 

 Latin word turbin is, of a whirlwind. 



Child. Why is this form of a shell named 

 after a whirlwind 1 



Teacher. Because the first sweep of a whirl- 

 wind describes a circle much larger than those 

 which succeed, when its power is in some degree 

 exhausted. Do you not now perceive how 

 applicable the term is to the form you were 

 describing ? 



Child. Yes. The body whorl is very large 

 in proportion to the others, just as the first sweep 

 of a whirlwind is large, compared with those that 

 succeed it. 



Teacher. You have now observed the general 

 appearance of the conus ; what particular part 

 were you to take into consideration, in order ta 

 draw out the generic character ? 



Child. The mouth. 



Teacher. And what do you observe in the 

 mouth of the cones ? 



Child. It is long and narrow. 



Teacher. When the mouth is very narrow in 

 proportion to its length, and also of a nearly 

 equal breadth throughout, it is called linear, from 

 its having the character of a line. In considering 

 the parts of an object, is it their form only that 

 strikes your attention I 



