2 28 ANIMAL AGGREGATIONS 



the survival in dialyzed Procerodes-conditioned water having the 

 same initial resistivity. 



HETEROTYPICALLY CONDITIONED WATER 



Having demonstrated in two successive years that Procerodes 

 may be protected, at least to some extent, from the harmful effect 

 of extremely hypotonic sea-water by being isolated in water condi- 

 tioned by exudates or watery extracts of other Procerodes, and that 

 whatever the protective device may be, it is not a direct result of an 

 increase in total electrolytes present, it becomes of importance to 

 inquire carefully concerning the specificity of this protection. 

 Evidence will be presented here concerning the species specificity 

 only, since to date no work has been done to attempt the analysis of 

 possible functional specificity. In the course of this study the effects 

 of the following kinds of media were tested against very dilute sea- 

 water with the same resistivity: Paramecimn culture medium, water 

 extract of Planaria maculata (a fresh-water turbellarian) and of P. 

 maculata culture media, and water extracts of a marine amphipod. 

 The effect of each of these will be discussed in the order given. 



Paramecium culture medium. — The solution used was the clear 

 brownish surface liquid from a hay infusion which contained a 

 vigorously growing and almost pure culture of Paramecium. The 

 general situation can be presented most clearly by describing one 

 experiment in some detail and by adding summaries of all. In 

 Experiment 74, hay-infusion liquid, such as has just been described, 

 containing many Paramecia was boiled and dialyzed against run- 

 ning tap-water until it showed a resistance of 6,450 ohms at 20° C. 

 Tap-water was brought to the same resistivity by adding 0.25 per 

 cent sea-water. Another lot of tap-water was brought to 5,450 ohms 

 resistance. 



One hundred and fifty Procerodes were isolated, 50 into each of the 

 modified tap-waters and 50 into the dialyzed Paramecium Q\AtVir& 

 medium. At the end of 6 hours the water in the more dilute tap series 

 had changed from 6,450 to 3,350 ohms and that in the culture me- 

 dium had fallen from the same initial level to 3,550 ohms. Both 

 were changed to 6,550 ohms in their respective media. After an- 



