210 ERNEST WARREN. 



health of the auimals reached a maximum. The resisting 

 power to the salt at this period was very great. Gradually 

 as the tank became crowded, the poisoning effect (further 

 evidence of this will be adduced later) of the close proximity 

 of large numbers of animals of the same kind came into 

 force. The Daphnia became sickly, and the resisting power 

 to the salt sank very low. This view is supported by the 

 further behaviour of the animals in the tank ; the crowd 

 of Daphnia died off, and after about a month only a com- 

 parative few remained. 



4. Experiments on the acclimatisation of Daphnia 

 magna to sodium chloride. 



a. History of the Y Family. 



October 19th. — Five individuals from the tank were placed 

 into '2 per cent. 



27th. — There was one survivor (= Y), and this had pro- 

 duced a brood (= Y a). Y and Y a were now placed into 

 "5 per cent, solution. 



November 3rd. — Ova appeared in the brood pouch of Y, 

 and they became red by the action of the salt. This proves 

 that the salt has a distinct chemical action, and that the 

 phenomena observed are not to be referred to merely the 

 density of the medium. 



15tli. — Y, Y a, Y ao were put into '55 per cent, solution. 



18th.— Y dead. 



24th. — All the animals dead. 



j3. History of the X Family. 



October 19th. — Five Daphnia from the tank were placed 

 into "5 per cent, solution. 



21st. — All five animals were dead, but a newly born indi- 

 vidual was alive and well. This was placed into a fresh 

 tumbler of '5 per cent., and labelled X. 



November 1st. — X produced a brood Xa ; two individuals 

 of this brood were placed into fresh water to act as a control. 



