No. 523] 



REPRODUCTION OF DAPHNIA 



405 



Effect of Environment on Differential Growth 



By differential growth I mean the nneqnal growth of 

 different parts, viz., the germ and body cells. Only 

 parthenogenetic females were used, and each was kept 

 separately in the same quantity of water. All measure- 

 ments were made at sexual maturity, i. e., when the 

 first eggs appeared in the brood pouch. Warren 3 found 

 that under uniform conditions there was a slight varia- 

 bility, but Woltereck showed that these fluctuating varia- 

 tions were very small, though he did find mutations as 

 rare occurrences. 



Nutrition. — I had in the laboratory a pure culture of 

 a unicellular green alga which the daphnids ate readily. 

 This alga did not remain entirely suspended in the water, 

 but as the daphnids fed on the bottom as well as while 

 swimming, and stirred up the algffi, it can not be said 

 that most of the food was out of their reach. 



Those with a superabundance of food were larger at 

 sexual maturity and had a shorter spine than those with 

 insufficient food, and conversely. The smaller size and 

 longer spine of the starved daphnids are characteristic 

 of immature stages. 



a "An Observation on Inheritance in Parthenogenesis,' 

 London, 1899, LXV, and "On the Reactions of Daphnia 



