CHANGES IN ENVIRONMENT OF DAPHNIA JIAGNA. 



209 



and none diecl^ while 75 per cent, of the Daphnia taken out 

 of the tank a few days previously died in four clays. 



Previous to the removal of the plants all the Daphnia 

 (except in one case where an individual survived and bred) 

 immersed into '5 per cent. NaCl died in thirty- six to forty 

 hours; but two days after the removal most of them lived 

 for ninety-six hours, while some survived and produced 

 young. During the following three weeks sets of ten indi- 

 viduals were repeatedly put into "5 per cent. NaCl^ and the 

 time when 100 per cent, had succumbed was noted. Tlie 

 results are given in the accompanying table. 



Removal of Vallisucilii 11 o'clock a.m., November 23rcl. 



The vigorous condition of the Daphnia on November 25th, 

 29th, and December Gth was followed by a rapid decadence 

 in the power of resisting the action of the salt. These large 

 and remarkable fluctuations in the resisting power seem to 

 point to the following conclusions. The removal of the 

 excessive vegetation was highly favourable^ to the Daphnia; 

 reproductive activity came into full swing, and the general 



' Tlie exact cause I am ciuleavourintj to ascertain at tl'C present time. I 

 am inclined lo think that tiie shadinix eU'ect and the g-recn lii^lit arc both pre- 

 jiulicial to the <.M\)\vth and reproductive power of Daphnia. 



