CHANGES IN ENVIRONMENT OE DAPHNIA MAGNA. 2ll 



The X family was living in 200 c.c. of solution, and 1 c.c. of 

 1 per cent, solution was now added on alternate mornings. 



4tli. — Eggs in brood pouch of X reddish, 



8th. — Xand X a were put into "525 per cent, solution. 



11th. — The eggs in brood pouch of X had become of the 

 ordinary dark colour. 



15th. — X, X a, X tto were put into "55 per cent, solution, 

 and no addition of salt was now made. 



18th. — X apparently well; the broods X a and X cto were 

 very slow in growing; the largest were not more than half 

 the size of the two control individuals which had been placed 

 into fresh water on November 1st. One of these two control 

 animals had produced two young on November 16th. 



23rd. — All dead ; the controls were perfectly healthy. 

 Thus in both the X and Y families it was not found possible 

 to acclimatise the animals to a solution above '55 per cent. 

 NaCl. The gradual increase in salinity from 'b per cent, to 

 "55 per cent, during a fortnight proved to be too rapid to 

 affect a thorough acclimatisation to '55 per cent. It is very 

 doubtful whether acclimatisation per se could be carried 

 much beyond this. 



5. Does acclimatisation to a certain strength of 

 solution increase the resisting power to a solution 

 containing a higher percentage of salt? 



Suppose an animal has been acclimatised to a certain solu- 

 tion of salt, say a per cent., and is then plunged into an x 

 per cent, solution, where x is greater than a, the question 

 arises whether the x per cent, solution would act on the 

 acclimatised animal like an x-^a per cent, solution on an 

 ordinary Daphnia from the tank. 



Thirty Daphnia ^ were taken from the tank and gradually 

 acclimatised (taking seventeen days in the process) to "25 per 

 cent, solution. None of the Daphnia died in the process. 



1 This was at the period when "2 per cent, solution killed 75 per cent, of 

 the auiiuals in four days. 



