224 ERNEST WAHKKN. 



The supposed poisoning effect of Daphnia on Daphnia is 

 not new in principle, and it lias considerable significance from 

 the point of view of epidemics, which so frequently arise 

 when from any cause one kiud of animal becomes excessively 

 abundant. 



In conclusion I wish to expi-ess my indebtedness to Pro- 

 fessor Weldou for his kind help and ready suggestiveness. 



