THE SNAIL 145 



bivalve ? How large was the animal when it began to build 

 this shell? The line around which the shell coils is called 

 the columella, and all the part included in the whorls is 

 called the spire. Draw shell. 



(3) Take an alcoholic specimen and break away the 

 shell to expose the lower part of the body. Find the parts 

 noticed before, and further up notice the respiratory orifice. 

 What relation has it to the mantle ? With a scalpel cut open 

 the orifice and find the structure of the interior? What 

 seems to be its origin and use? What is the advantage in 

 having it located at the edge of the shell? 



(4) Find the mouth. Note its position, size and shape. 

 Cut open the flesh surrounding it and look for teeth. What 

 is the use of that ribbon-shaped tongue? Remove it entire 

 with the muscles at either end. It is called the radula, and 

 works by moving back and forth like a handsaw. Draw 

 entire radula with muscles. Put a piece of it under the 

 microscope and observe the teeth. Draw. 



The systems of digestion and reproduction are situated 

 up in the spire of the shell, with openings near the mantle 

 rim. 



Reproduction. — The eggs are laid in thin transparent 

 capsules, and may be found in the aquarium where the 

 snails are kept for a short time. These may be studied 

 in a watch crystal under the low power of the microscope, 

 and their development watched from day to day. The 

 shell appears as a cap on a small matrix, and continues 

 to enlarge until it covers the animal, after which it coils 

 as the animal grows. Under the direction of the teacher 

 this life history of the snail becomes a very interesting and 

 profitable study. 



STU. IN ZOOL. — 10 



