230 ANIMAL AGGREGATIONS 



with the same resistivity as the culture medium, while Control II 

 designates the less-dilute salt solution. 



The summary shows that the worms in the culture medium lived, 

 on the average, 25.85 hours, while those in the very dilute sea- water 

 with the same initial resistivity lived only 15.2 hours. The differ- 

 ence of 10.65 hours, when examined by Student's method, shows a 

 statistical probabihty of 0.0714, when considered as 5 pairs of tests 

 as listed above, but when considered as 49 individual pairs, the 

 probability becomes 0.00002, which is clearly significant. 



As convincing as is this experience that Paramecium culture me- 

 dium with equal or less total electrolytes than accompanying dilute 

 sea- water has a survival value for marine Proccrodes isolated into it, 

 the same series of experiments furnished still further evidence that 

 such is indeed the case. In the series labeled "Control II" the initial 

 resistance was 1,000 ohms less, and therefore a less-dilute solution 

 of sea-water than Control I. This water was renewed each time the 

 others were changed, and was kept at least 1,000 ohms more con- 

 centrated at these times. It was never found to be less concen- 

 trated than was the culture medium, and only once to have the same 

 concentration. The worms in this less-dilute sea-water lived longer 

 than did those in Control I by an average time of 4.1 hours, a dif- 

 ference which is not statistically significant. 



The worms in the culture medium showed a mean survival time of 

 6.55 hours greater than did those in the more concentrated Control 

 II. When individual pairs are considered, this has a probability of 

 0.02, and hence is statistically significant. Further experiments 

 with Paramecium culture medium and with water extracts and 

 culture medium of Planaria maculata, and water extracts of marine 

 amphipods found in close association with Procerodes in nature, give 

 essentially the same results and show that heterotypically condi- 

 tioned fresh water has protective value for Procerodes isolated into 

 it as compared with the survival when isolated into hypotonic sea- 

 water with the same electrical resistivity. 



While this general relation holds, there was not necessarily the 

 same degree of protection from each type of solution. Whether this 

 is due to the conditions under which the experiments were run, or 



