PREFACE 



IN THE following pages we have endeavored to present a 

 brief and untechnical account of fresh-water life, its forms, 

 its conditions, its fitnesses, its associations and its economic pos- 

 sibilities. This is a vast subject. No one can have de- 

 first hand knowledge in any considerable part of it. Hence, 

 even for the elementary treatment here given, we have borr 

 freely the results of researches of others. We have selected out 

 of the vast array of material that modern limnological studies 

 have made available that which we deem most significant. 



Our interests in water life are manifold. They are in part 

 economic interests, for the water furnishes us food. They are 

 in part aesthetic interests, for aquatic creatures are wonderful to 

 see, and graceful and often very beautiful. They are in part 

 educational interests, for in the water live the more primitive 

 forms of life, the ones that best reveal the course of organic evolu- 

 tion. They are in part sanitary interests; interests in pure 

 water to drink, and in control of water-borne diseases, and of 

 the aquatic organisms that disseminate diseases. They are 

 in part social interests, for clean shores are the chosen places for 

 water sports and for public and private recreation. They are 

 in part civic interests, for the cultivation of water products for 

 human food tends to increase our sustenance, and to diversify 

 our industries. Surely these things justify an earnest effort to 

 make some knowledge of water life available to any one who may 

 desire it. 



The present text is mainly made up of the lectures of the senior 

 author. The illustrations, where not otherwise credited, are 

 mamly the work of the junior author. Yet we have worked 

 jointly on every page of the book. We are indebted for helpful 

 suggestions regarding the text to Professors E. M. Chamot, G. C. 

 Embody, A, H. Wright, and to Dr. W. A. Clemens. Miss Olive 

 Tuttle has given much help with the copied figures. 



21978 



