296 R. G. Stress et al. 



the other extreme the particles would clog the feeding system and actually 

 reduce the efficiency of assimilation. 



D. middendorffiana possesses an endogenous rhythm of feeding 

 activity. Animals held under constant light and temperature had peaks of 

 feeding at 1400 and 2400. This could be a strategy for optimizing feeding, 

 for these are the same hours that the water temperature in the natural 

 pond on a clear day is optimum for feeding for this species. 



The population of Daphnia hatch from the overwintering eggs in a 

 single burst which lasts for 2 or 3 days. This synchrony is retained 

 throughout the lifetime of the population as the single brood of eggs all 

 appeared within a 4-day period and these eggs also hatched in a rough 

 synchrony. There was also synchrony of molting within a part of a single 

 day but a circadian rhythm could not be demonstrated. 



