Marsh — The Plankton of Fresh Water Lakes. 181 



nation, and lience the conditions of the bottom are more favor- 

 able for animals than in a small lake. The larger the lake, then, 

 other conditions being eqnal, the greater would be the abundance 

 of abyssal life. While there have been no accurate means of 

 comparing the abyssal fauna of the Great Lakes with that of the 

 smaller lakes as to quantit}^, such collections as have been made 

 would indicate that it is much greater in the Great Lakes, and 

 decreases in proportion to the degree of stagnation. If my ex- 

 planation proves to be the correct one, as I feel quite certain it 

 will, it will follow that the small deep lake will be limited in its 

 fauna in two ways : because of its steep shores it will have a 

 small littoral fauna and flora, and because of its stagnant deep 

 water it will have little or no abyssal fauna. 



I have thus far spoken as though all lakes had the three 

 f aunse : littoral, limnetic, and abyssal. Generally speaking this 

 is true, even small bodies of water showing this distinction. But 

 occasionally the distinction is almost lost. This is true in Lake 

 AVinnebago. In spite of its great size — the lake is some twenty- 

 eight miles long by ten or twelve broad at its greatest width — • 

 it is only about twenty-five feet deep. In its fauna there is a 

 curious mingling of littoral and limnetic forms, littoral forms 

 being found in the open lake, and limnetic forms even among 

 the weeds along shore. The exj)lanation seems to be this: be- 

 cause of its slight depth the environment, even far from shore, 

 is favorable to the growth of littoral fonns. Then there is a'ood 

 reason for thinking that the w^inds have a profound effect on its 

 waters, thus thoroughly mixing limnetic and littoral waters, and 

 consequently causing a similar mingling of the organisms. Lake 

 Winnebago has the characteristics, in many respects, of an enor- 

 mously overgrov.m puddle. I do not say this, however, to show 

 a lack of respect for this lake, for from a practical standpoint 

 it is a most valuable possession to the state. It can support, and 

 does support, an enormous number of fish. Few lakes can com- 

 pare wnth it in productiveness. 



All the inhabitants of fresh water are, of course, descendants 

 of marine forms. In some cases the modifications have been 

 very great bur in others they are hardly to be distinguished 

 from their salt-water relatives. This is true, as has already been 



