62 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



a large part in producing differences in lake faunae. The 

 chance planting of certain forms may determine the character 

 of the fauna for a long period. Everything in Green lake 

 would seem to favor the growth of Cyclops pulchellus as the 

 limnetic form of Cyclops. That it does not exist there, it seems 

 to me, must be simply because it has not been planted, and there 

 is no way it can reach that lake except through the agency of 

 water-fowl. Diaptomus siciloides in some way got a foothold 

 in Cedar lake, and remains there because of its isolation and is 

 not carried to other lakes, because there are not suitable connect- 

 ing bodies of water. 



I have noted in a former paper (Marsh '95), that Diaptamus 

 Reigliardi was found only in a few lakes in the northern part 

 of the southern peninsula of Michigan. If water-fowl readily 

 carried entomostraca from one body of water to another, it 

 would seem very strange that this species should not appear in 

 the lakes in northern Wisconsin, instead of being confined to 

 such a narrow habitat. It is noticeable 1 , too, that Diaptomus 

 Reighardi in Michigan is, for the most part, found in lakes 

 closely connected with each other. 



It appears, then, that isolation caused by the physical con- 

 figuration of the country will tend to' produce distinct differ- 

 ences in plankton constituents, in spite of the other causes which 

 may be at work to' distribute animals and plants. 



COMPARISON OF THE FAUNAE AND FLORAE OF DIFFERENT 

 CLASSES OF LAKES. 



The preceding subject, leads naturally to the question of the 

 faunal and floral distinctions between the different classes of 

 lakes. The classification, as made in the earlier part of thia 

 paper, was based on physical distinctions which must affect 

 the environment and produce characteristic differences in the 

 animals and plants. As a matter of fact it was such differences 

 which first led me to suggest the division of lakes into deep and 

 shallow. 



