42 LESSON VIIL 



Teacher. Can you tell me what is tlie 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, and from hence their 

 name valve. 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 mult us, t he 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, before they 

 proceed to a new part. 



1. Describe the animals called mollusks. 



2. Which of the different senses do they 

 possess ? 



3. How do they move on land ? 



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



5. Describe the different methods by which 

 they render themselves stationary. 



