6 ELIZABETH LOCKWOOD THOMPSON 



several instances this mucus was observed to touch the mouth 

 parts and such contact was followed b}^ reactions. These are 

 noted in the following table. Stimulation of this sort is the 

 probable cause of all other reactions that occur in the test series. 



TABLE I 



Showing the number of reactions of the mouth of six individuals of Physa gyrina 

 Say, kept under observation in filtered tap water for 32.75 hours, when not stim- 

 ulated by the application of food to the mouth region. The snails had been with- 

 out food for 24 hours preceding the tests. They were divided into two groups of 

 three each and tested on alternating days. 



* Indicates that an egg mass had been deposited within the 24 hours preceding 

 the test. 



