WM. A. KEENER AND W. H. TALIAFERRO. 



compared with the specimens of Group l-a, in that they pass 

 through the drop of .05 per cent, salt solution instead ot turning 

 away from it. 



Group 2-b (specimens placed in .05 per cent, salt solution and 

 allowed to encounter a drop of fresh water). 



December 16, 1911. A specimen that had been kept in the 

 laboratory three days entered the fresh water three times but each 

 time it left it without showing any reaction to the salt solution 

 (text-figure 9-0). 



January 9, 1912. A specimen that had been in the laboratory 

 four days entered the fresh water three times but each time it 

 left it (text-figure 9-^). 



Novembei- 20, 1911. A specimen that had been in the labora- 

 tory five days entered the fresh water three times but each time 

 left it (text-figure 9-c). 



FIG. 9. Diagrams indicating the paths of specimens when placed in .05 per cent, 

 salt solution and encountering a drop of fresh water. The dotted line indicates 

 the contour of the drop of fresh water surrounded by .05 per cent, salt solution. 



These specimens, too, show a marked contrast with Group i-b 

 in that they pass indifferently from .05 per cent, salt solution into 

 fresh water and back into the .05 per cent, salt solution instead of 

 remaining in the drop of fresh water. 



Thus our experiments have sustained the inference that the 

 physiological condition of Microstoma is lowered by the condi- 

 tions peculiar to laboratory aquaria. This loss of physiological 

 tone generally takes place after the first twenty-four hours. 



The conditions most strikingly peculiar to laboratory aquaria 



