46 LESSON VII. 



Teacher. These distinct pieces are called 

 valves. Where have you ever heard of a valve ? 



Child. A pump has a valve, and steam 

 engines have valves. 



Teacher. Can you tell me what is the use of 

 the valve of a pump ? 



Child. To prevent the water from returning 

 into the pipe through which it has passed. 



Teacher. The animals of these shells with 

 two valves use these pieces for a very similar 

 purpose, to exclude the water. Now that you 

 have found out the distinguishing character of 

 these classes, I will give you their names.. 

 Those shells which are composed of only one 

 valve are called univalves, from the Latin, un us, 

 one, and valve. Shells composed of two valves 

 are called bivalves, from bis, the Latin for twice, 

 and valve. Shells composed of more than two 

 valves are called multivalves, from multws, the 

 Latin for many, and valve. 



QUESTIONS ON THE MOLLUSCA 

 AND THE SHELL. 



Questions will be given at each division of the subject, which 

 the children should be able to answer well without assistance, 

 before they proceed to a new part. 



1. Describe the animals called mollusca. 



2. Which of the different senses do they 

 possess 1 



3. By what means do they advance on land ? 



4. By what means do they advance in the sea? 



