Marsh — Limnetic Crustacea of Green Lake. 217 



GENERAL CONCLUSIONS IN REGARD TO VERTICAL DISTRIBUTION. 



I had supposed that there was a general movement of the 

 whole body of Crustacea in such vertical migrations as existed. 

 It is evident that this is not the case, for the different kinds 

 have their individual peculiarities of distribution. 



In the case of Diaptomus there is little or no vertical migra- 

 tion from any cause. 



Epischura avoids bright light, and has a preference for warm 

 water, and shows both seasonal and diurnal migrations. 



IAmnocalanus is repelled by bright light and by a high tem- 

 perature, hence its diurnal migration is more pronounced in 

 cold weather. 



Cyclops brevispinosus occurs most abundantly between five and 

 twenty meters in depth. I have no evidence in regard to its 

 diurnal migrations. 



Cyclops fluviatilis has no diurnal migration, but in its seasonal 

 distribution shows a preference for the warmer water. 



Leptodora is a surface form. I have no conclusive evidence 

 in regard to its diurnal migrations. 



Daphnia kahlbergienses apparently moves towards the surface 

 at night. 



There is no appreciable difference in the seasonal distribution 

 of Bosmina. There is a distinct diurnal migration due to its 

 attraction to light. 



Daphnella has a diurnal migration due to the fact that it is 

 repelled by light. 



I cannot make out from my collections that the winds have 

 any effect on the vertical distribution of entomostraca. The dis- 

 tribution when the surface is roughened by waves seems to be 

 practically the same as when it is smooth. Neither is there 

 any marked difference between dark and moonlight nights. 



It must be remembered, however, that all my collections were 

 at five meter intervals, and that there may be migrations within 

 these limits of which I have no indication. I know for instance 

 from surface tows that the immediate surface is almost entirely 

 devoid of entomostraca in the day time, but is populated in 

 enormous numbers in the night. There is evidently a very 



