94 



W. C. ALLEE. 



TABLE I. 



SHOWING MAXIMUM-MINIMUM WATER LEVEL ANALYSES OF WATER FROM COUNTY 

 LINE CREEK, BRAESIDE, ILL., AND SLOUGH 93, OSBORN, IND. 



The solids are shown in parts per million by Mariner and Hoskin's analyses 

 and the gases in c.c. per liter. 



equivalent of the amount of calcium contained in o.on normal 

 solution of calcium chloride. Supposing for the moment this 

 calcium were the only cation present in the water it would have 

 no depressing action on rheotaxis. 



Witness: 



Isopod 146 gave a rheotactic reaction of 30 per cent. + , 50 

 per cent. --,24 per cent, a when first tested and after being in 

 0.05 normal solution of calcium chloride for five days the rhe- 

 otactic response was 90 per cent. + , 10 per cent. . 



Isopod 147 when first tested gave 60 per cent. +, 10 per cent. 

 -, 30 per cent. a. and after 48 hours in a similar solution of cal- 

 cium chloride gave 40 per cent. +, 30 per cent, a, 30 per cent. o. 



Three other isopods (Nos. 175, 176, 177) after 10 days in the 

 same strength calcium chloride solution gave an average re- 

 sponse of 37 per cent. +, 30 per cent, a, 33 per cent, o while the 

 average rheotactic reaction of 253 untreated isopods from similar 

 environmental conditions was 31 per cent. +, 45 per cent. -, 

 22 per cent, a, 2 per cent. o. 



But calcium is not the only cation present. Magnesium, a 

 less powerful isopod depressant than calcium, is found to the 

 extent of 0.0037 normal solution. If at this strength magnesium 



