CHANGES IN ENVIRONMENT OF DAPHNIA MAGNA. 203 



constant temperature. A solution containing a definite per- 

 centage of salt was taken and five Daphnia were simultane- 

 ously placed in it, and the time elapsing before tlie last 

 flickering movements of tlie limbs stopped was noted. Some 

 of the animals were found to succumb much quicker than 

 others. This experiment was performed five times with the 

 same strength of solution. Thus the longest period recorded 

 out of the five trials was the time in which all the animals out 

 of the twenty-five had either died or passed into the condi- 

 tion of salt-rigor. The twenty-five Daphnia were treated in 

 detachments in this way, because it was found impossible to 

 examine with suflEicient exactness and speed more than five 

 individuals. 



The results are summed up in the following table : 



Table I. — Daphnia magna from the tank at Univer- 

 sity College, London, October, 1897. Tempera- 

 ture during experiments = 21° C. 



* In this batcli it took fifteen clays to kill one of the Daphnia, and it, seems 

 to nie doubtful liow far the salt was the cause of its death. 



