272 BULLETIN OF THE BUREAU OF FISHERIES. 



can see no answer except — mud. The thick layer of soft mud on the bottom of Lake 

 Mendota is rich in organic materials and contains a very abundant fauna of detritus 

 feeders.^ The mud and its animals form an enormous store of organic material. This 

 makes aquatic plants and plankton abundant; this in turn gives opportunity for fishes 

 (silversides, etc.) which feed on pelagic organisms to flourish and makes those which 

 feed on plants and small fishes more abundant. Green Lake is a fine, healthful habitat 

 for fishes in somewhat the same way that a desert on land is healthful. Its possibilities 

 are limited because it lacks mud. Rich "soil" is just as important for raising animals 

 from aquatic pastures as it is for those on land. Petersen (19 18) has recently made a 

 similar generalization in regard to the ocean. ^ 



BIBLIOGRAPHY. 



BiRGE, Edward A. 



1897. Plankton studies on Lake Mendota. II. The Crustacea of the plankton from July, 1894, 

 to December, 1916. Transactions, Wisconsin Academy' of Sciences, Arts, and Letters, 

 VoL XI, 1896-97, pp. 274-448. Madison. 

 BiRGE, Edward A., and Chancey Juday. 



1911. The inland lakes of Wisconsin. The dissolved gases of the water and their biological sig- 

 nificance. Wisconsin Geological and Natural History Survey, Bulletin No. XXII, 

 Scientific Series No. 7, xx+zsg pp. Madison. 

 Juday, Chancey. 



1914. The inland lakes of Wisconsin. The hydrography and morphometry of the lakes. Wis- 

 consin Geological and Natural History Survey, Bulletin No. XXVII, Scientific Series 

 No. 9, xv-l-137 pp. Madison. 

 Marsh, C. Dwight. 



1903. The plankton of Lake Winnebago and Green Lake. Wisconsin Geological and Natural 

 History Survey, Bulletin No. XII, Scientific Series No. 3, vi-l-94 pp. Madison. 

 PearsE, a. S. 



1918. The food of the shore fishes of certain Wisconsin lakes. Bulletin, U. S. Bureau of Fisheries, 

 Vol. XXXV, 1915-16, pp. 247-292. Washington. 

 PEarsE, a. S., and Henrietta Achtenberg. 



1920. Habitsof yellow perch in Wisconsin lakes. Bulletin, U. S. Bureauof Fisheries, VoL XXXVI, 

 1917-18, pp. 293-366. Washington. 

 Petersen, C. G. Joh. 



1914. Valuation of the sea. II. The animal communities of the sea bottom and their importance 



for marine zoogeography. Report, Danish Biological Station, Vol. XXI, 1913, 42-f-68 

 pp. Copenhagen. 

 1918. The sea bottom and its production of fish food. A survey of the work done in connection 

 with valuation of the Danish waters from 1883-1917. Ibid., Vol. XXV, 1918, 82 pp. 

 Petersen, C. G. Joh., and P. Boysen Jensen. 



1911. Valuation of the sea. I. Animal life of the sea bottom, its food and quantity. Report, 

 Danish Biological Station, Vol. XX, 1911, 8i pp. Copenhagen. 

 Reighard, J. 



1915. An ecological reconnoissance of the fishes of Douglas Lake, Cheboygan County, Michigan, in 



midsummer. Bulletin, U. S. Bureau of Fisheries, Vol. XXXIII, 1913, pp. 215-249. 

 Washington. 

 Wagner, George. 



1911. The ciscoof Green Lake, Wisconsin. Bulletin, Wisconsin Natural History Society, Vol. IX, 

 pp. 73-77. Milwaukee. 



' Birgeand Juday have found as many as 30.000 Corethralan'fe per square meter in the n]ud on the bottom of Lake Mendota. 



3 Dr. R. E. Coker, after reading the manuscript for this paragraph, suggests that the richness of food stores in a lake may 

 perhaps be connected with the fertihty of the soil in the surrounding drainage area. Dr. R. H. Whltbeck, professor of geography 

 in the University of Wisconsin, assures the writer that the drainage basin of Green Lake is less fertile than that of Lake Mendota. 



