174 
in a comparison of the seasonal distribution of these more decidedly 
spinous varieties of B. bakert with that of the smoother forms, such 
as clumorbicularis, 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. bakert 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 alge 
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 
