THE BIOLOGY OF PHYSA. 



The present work is an attempt to study one of the lower 

 animals, the common pond snail, in the field and laboratory 

 by both observational and experimental methods. The work is 

 divided into the following parts all of which are interdependent : 

 I. .The relation of Physa to its natural environment, II. Mucus 

 and Mucous Threads, III. Food and food activities, IV. Respi- 

 ration of Physa, and V. Some psychic phenomena of Physa. 



The work was begun at the University of Michigan and w^as 

 completed at Clark University. Grateful acknowledgments 

 are due to the following people for assistance: Professor Jacob 

 Reighard for general supervision of the work. Dr. Charles C. 

 Adams for supervision and for liberal aid in the preparation 

 of part I, " The relation of Physa to its natural environment," 

 Professors H. S. Jennings and C. F. Hodge for invaluable sug- 

 gestions in the final preparation of the manuscript, and Mr. 

 Bryant Walker for the identification of the snails. 



I. THE RELATION OF PHYSA TO ITS NATURAL 

 ENVIRONMENT. 



I. Introduction. 

 II. Local distribution. 



III. The Brook-Creek-River System as a habitat. 



1. Springs and brooks. 



a. Brooks. 



b. Brook-ditches. 



2. Creeks. 



a. Creek beds. 



b. Shallow eddies. 



3. Rivers. 



4. Discussion of the river system as a habitat. 



IV. Lakes, Ponds and Swamps as habitats. 



1. Lake. 



a. Beach pools. 



b. Ice rampart pools. 



c. Open sedge forinations. 



d. Spit and bar formations. 



e. Open .shores. 



2. Discussion of the lake as a habitat. 



3. Ponds and swamps. 



a. Relation of pond weeds to Physa. 



I. Optimum Chara habitat. 

 II. Optimum Ceralophyllurn habitat. 



III. Optimum Hypnum habitat. 



IV. Optimum Elodea habitat. 



b. Relation of drought to pond weeds and Physa. 



c. Relation of drought to Physa or snail desiccation. 

 V. General Summary and Discussion. 



