240 



to year, is therefore of prime importance in the search for the causes of the 

 differences in the same fish in two contiguous lakes or in two successive years in 

 the same lake. 



Our plankton apparatus was completed too late to enable us to make any 

 systematic measurements, especially as our planktonist was actively engaged in 

 the physical survey of the lake. But plankton was collected and some of its 

 different constituents will be reported upon. 



A good historical account of planktonic studies, as well as exact definitions, 

 are to be found in the Planktonic Studies of Haeckel, translated by G. W. P'ield, 

 and published in Commissioners' Report, 1889-91, U. S. Com. Fish and Fisheries, 

 pp. 565-641. 



In the following sketch several groups of animals are not at all considereds 

 and others but briefly. The only groups found in the lake of which we approxi- 

 mate a complete list are the fishes, batrachians and reptiles. Deficiencies will be 

 removed in subsequent reports when a classification of the material into litloral, 

 hathyhial and pdrnpc will also be attempted. 



The Protozoa were not represented by a large array of species d uring the summer. 

 No detailed work has been done on them as yet, but I want to mention two 

 characteristic forms. 



The most striking Protozoan is Ophridium. It is found in clumps varying from 

 microscopic minuteness to the size of walnuts, and in different parts of the lake 

 the pebbles and exposed parts of clam shells are covered with these colonies to 

 such an extent as to suggest young lettuce beds. 



Cerutium hirudinella is as striking and abundant in the prkujic regions as 

 Ophridium is in the littoral. 



In this connection two plants may also be noticed. 



PIridaria is very abundant during the whole summer. It is conspicuous in 

 calm weather, when it rises to the surface. Toward the end of August and in 

 early September it collects in such numbers as to form large patches and streaks, 

 forming a true M^tJiserhliithe. 



Various forms of Paimella are abundant during the whole summer, and in 

 October, when Rivalaria has disappeared, it forms large patches on the surface 

 forming the WasserblHthr of the late fall. 



