12 FRESH-WATER BIOLOGY 



tributions to the general and special problems of fresh-water 

 biology. 



Fresh-water biological stations have aided by organized effort 

 the conquest of the field. The activities of the Illinois State 

 Laboratory of Natural History on the lUinois river, of the Wis- 

 consin Geological and Natural History Survey on the lakes in that 

 state, of the U. S. Bureau of Fisheries on the Mississippi, of Ohio 

 State University on Lake Erie, of the University of Montana 

 Biological Station on Flathead Lake in the Rocky Mountains, 

 show the variety and scope of these interests. Unfortunately 

 only the first three are active all the year through. Other uni- 

 versities, notably Michigan, Lidiana, Iowa, Colorado, North 

 Dakota, and Cornell, have participated in the study of fresh-water 

 life during part of the year or for a short series of years, and much 

 emphasis has been laid upon the lake biological station as a factor 

 in teaching biology. Few of these enterprises have had contin- 

 uous existence or permanent support. Such institutions are slowly 

 but surely gaining ground; their future development will aid both 

 the investigations of pure science and the appHcation of such dis- 

 coveries to the solution of practical problems. The significance 

 for man of the problems outlined in this chapter and their bearing 

 upon the progress of social development have been discussed in 

 the final chapter of the book. 



Save insects which moreover are primarily terrestrial forms, no 

 type of fresh-water life has developed to the diversity and com- 

 plexity attained by the same type in the ocean. Yet each type 

 has achieved a variety well illustrated in the subsequent chapters. 

 Only a few of those that occur in the ocean are unrepresented in 

 fresh water and even strictly terrestrial groups like the mammals 

 and flowering plants or aerial forms like birds have their aquatic 

 representatives. In subsequent chapters each of these groups is 

 discussed from the biological standpoint and in its especial rela- 

 tions to fresh-water life as well as with regard to its relative impor- 

 tance as a factor in the fresh-water flora and fauna. 



The records of science contain only scanty references to the 

 types of fresh-water life and their distribution on the North Amer- 

 ican continent, and regarding all other continents save one the 

 records are even more fragmentary. Of Europe alone is the in- 



