240 



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

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

 tlie same lake. 



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

 systematic measurements, especially as our ])lanktonist 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 pulilished in Commissioners' Report, 1889-91, U. S. Com. Fish and P'isheries, 

 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 sul)sequent reports when a classification of the material into littoral, 

 bathybial and prlar/ie will also be attempted. 



PROTOZOA. 



Tlie Protozoa were not represented by a large array of species during 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 Ophruliion. 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. 



Ceratium hirndinella is as striking and abundant in the pelaxjic regions as 

 Ophridiiriii is in the littoral. 



In this connection two plants may also be noticed. 



Rivuluria is very abundant during tlie 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 Wa-iHcrhliitlw. 



Various forms of Palmella are abundant during tlie whole summer, and in 

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

 forming the WaaserbUithe of the late fall. 



