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in a comparison of the seasonal distribution of these more decidedly 

 spinous varieties of B. bakeri with that of the smoother forms, such 

 as cluniorbicularis , which indicates any correlation with temperature 

 conditions of a nature to support Wesenberg-Lund's suggestion 

 that the elongation of the processes of plankton organisms arises in 

 response to the lessened buoyancy of the water during higher tem- 

 peratures. Forms with and without such processes are found among 

 the varieties of this species, and both occur indiscriminately through- 

 out the whole range of seasonal occurrence, and, so far as I can see, 

 the statistical data of their distribution with respect to temperature 

 afford no evidence of a correlation of spinosity and high tempera- 

 tures in this species. Other factors doubtless enter into this 

 problem and obscure this response if it exists. 



B. bakeri is everywhere widely distributed in fresh water. Its 

 occurrence in the plankton of open waters has not, however, been a 

 matter of frequent note. In fact there is some reason to think that 

 it is largely confined to shallow warm waters where vegetation is 

 close at hand, or where at least the flagellates and smaller algae 

 abound, as they do in water fertilized by decaying vegetation or 

 other organic matter. There is, it seems, no reason for regarding 

 this species as merely adventitious in our plankton. It bears all the 

 characteristics of a true limnetic organism in our environment. Its 

 presence in the plankton is not due to floods or other disturbances 

 which might carry it from a littoral region into the open water. It 

 exhibits characteristic pulses, and is found everywhere in summer 

 in company with typical planktonts in open water. 



Zacharias ('98) records it in some German ponds and streams, 

 and Weber ('98) in Swiss marshes in the warmer months. Stenroos 

 ('98) also finds it in the summer plankton of littoral and open waters 

 in the shallow Nurmijarvi Lake in Finland. Jennings ('00) reports 

 it as one of the commonest rotifers in East Harbor, Lake Erie, and 

 in the swamps on the islands. In land-locked pools short-spined 

 varieties were found, and in swamps the long-spined. Speaking of 

 this difference, Jennings says " Possibly the different form found in 

 these pools is due to the greater concentration of various salts in this 

 water or to some kindred factor." In our own region both varieties 

 occur at the same time in the same environments, channel and 

 backwaters alike, and such factors as Jennings suggests to explain 

 the appearance of the varieties cannot well be operative here in 



