DISCUSSION OF RESULTS. 57 



rounded by weeds, and it was noted at the time of the collection 

 that the water was remarkably clear, although in most parts of 

 the lake it was quite opaque because of the presence of vegetable 

 matter. 



In Shawano lake the variation was somewhat greater than in 

 Winneconne and Pbygan. Shawano varies more in its depths, 

 but otherwise the conditions are much as in other lakes. 



It was from the collections made on Lake Winnebago, how- 

 ever, that I hoped for the most conclusive results. These were 

 made in considerable numbers and at such widely separated lo- 

 calities that it seemed to me it would be a fair test of the uni- 

 formity of horizontal distribution. 



I have placed in the foregoing table the amounts of plankton 

 obtained in Lake Winnebago on seven different days when col- 

 lections were made at several locations. The amount of uni- 

 formity is certainly very remarkable, and was, I must confess, 

 somewhat disheartening to me, for I had a theory to maintain. 

 The variation does not, in any case, exceed the limits which 

 Hensen says are compatible with uniformity, as he defines the 

 term. 



In former papers (Marsh '97, and Marsh '01), I have dis- 

 cussed this subject in detail, but the results of these collections 

 in Lake Winnebago and adjoining waters have led me to modify 

 somewhat the opinions then expressed, although I think they 

 were, in the main, correct. There seems to be no question that 

 in Lake Winnebago the horizontal distribution of the plankton 

 is practically uniform. How then can I explain the results of 

 collections as given in my former paper (Marsh '97) ? In 

 the former paper I was discussing only Crustacea, and came 

 to the conclusion that some of them were at times present in 

 aggregations which might be called swarms. These aggrega- 

 tions have been noticed by other observers, as for example 

 Birge (Birge '97, 371). 



I acknowledge now that I have, in the past, attached too much 

 importance to Crustacea as an element in the plankton. As 

 will be shown later, the controlling element in the amount of 



