g3 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



tion when they have almost disappeared in Lake Winnebago. 

 May it not be, then, that Green lake may have as much of that 

 part of the plankton that is useful for food for fishes as Lake 

 Winnebago? I have not facts, from my study of Wisconsin 

 lakes, to prove this, but it seems to me to be at least a reasonable 

 conjecture. It is a somewhat significant fact to me that Stone 

 lake is considered one of the best fishing lakes in the northern 

 part of this state, and it is one of the deeper lakes, being nearly 

 eighty feet in depth. It is true that Green lake is not a par- 

 ticularly good lake for fishing at the present time, but this is 

 probably because it is, to a considerable extent, "fished out." 



There is doubtless a difference between large and small deep 

 lakes in favor of the larger lake in productiveness. As I indi- 

 cated in a former paper (Marsh, '97, p. 180), this may be ex- 

 plained by the more complete stagnation in the abyssal waters 

 of the small deep lake. In the larger lake, in which the winds 

 have better play, the waters are piled up by the prevailing 

 winds at one end of the lake and return, in part, at least, by 

 bottom currents, thus aerating to some extent the abyssal re- 

 gions. This may explain the productiveness of Stone lake, for 

 it is a long, narrow body of water extending in a direction from 

 north to south and frequently violently disturbed by southwest 

 winds which prevail in this location. It is probable that its 

 abyssal regions are much less stagnant than, for instance, those 

 of the Chain o' Lakes which are still deeper, but smaller, and 

 surrounded by elevations which cut off the wind. I do not 

 think it probable that, under similarly favorable conditions, 

 deep lakes are ever as productive as the shallower ones, but I 

 think the difference between the two' has been much exagger- 

 ated. 



In a deep lake the littoral, limnetic, and abyssal regions are 

 quite sharply distinguished. There is, of course, no distinct 

 dividing line between the littoral and limnetic regions, and the 

 organisms of one may be found in the other, and yet the differ- 

 ence between the fauna of the central regions of a lake and its 

 shore is very marked. In a very shallow lake there is no true 



