212 ERNEST WARREN. 



Thirty other Daphnia from the tank were made to live 

 under exactly similar conditions as the animals being accli- 

 matised, except that no salt was added to tlie water. These 

 individuals were for the purpose of actiug as a control. 



(1) Ten apparently healthy acclimatised Daphnia and ten 

 control animals were plunged, into separate tumblers of 1 per 

 cent, solution. The acclimatised individuals "died" in eigli ty- 

 eiglit minutes, and the ten control Daphnia in ninety-eight 

 minutes. Now if the 1 per cent, solution had acted on the 

 acclimatised animals like (1— '25) per cent. = '75 percent, 

 solution on ordinary Daphnia, they ought to have lived for 

 hours, but we see that they resisted the salt less well than 

 the Daphnia which had been living in fresh water. 



(2) Ten acclimatised and ten control Daphnia were plunged 

 into 1"2 per cent.; the former succumbed in thirty-five 

 minutes, and the latter in fifty -eight minutes. Thus, a 

 result similar to that of the first experiment was obtained. 



It should be added that the Daphnia acclimatised to *25 per 

 cent, solution were perfectly healthy in appearance, and in 

 fact more so than the control individuals living in f i-esh water, 

 for some of the latter had died, and for some unknown reason 

 they did not seem in a very healthy condition. 



II. The Reaction of Daphnia magna to a Confined Volume 



OP Watee. 



The second series of experiments deals with the effect of a 

 small body of water on a certain dimension, and on the 

 power of growth and. reproduction ; incidentally some remarks 

 will be made on the eifect of a sudden transfer from one kind 

 of water to another. 



1. The influence of a confined volume of water 

 on the length of the spine. 



The '' spine " is formed by the posterior prolongation of 

 the carapace. Fig. 3 a represents an ordinary Daphnia 

 with a moderately long spine. 



Professor Weldon poiuted out to me that in all compara- 



