

54 NATHAN FASTEN 



One persisted in remaining here, while the other copepod darted 

 back into the lighted side of the dish. About three minutes 

 later the organisms died. 



The following evening this same experiment was repeated. 

 When the concentration reached 1.7 per cent, two copepods 

 became negative. One of these became positive again. The 

 concentration of the solution was now increased until it reached 

 a strength of four per cent, but the copepods behaved as before, 

 one remaining negative, while the others were positive. Every 

 now and then one of the positive three would dart away from 

 the light, but the next moment it would again become positive. 

 The copepods were not killed in this solution in thirty minutes. 

 We thus meet a parallel with that noticed in the discussion of 

 the reaction to copper sulphate, — a difference in the physio- 

 logical state of the copepods. 



Hydrogen peroxide. — This chemical caused a distinct reversal 

 in the behavior of the animals to light. When the water became 

 a nine per cent solution of the chemical, all of the copepods, 

 which up to this time had been darting about in the lighted 

 regie n, suddenly reversed their direction and began to move 

 away from the light. One died almost instantly, while the 

 other three traveled about three-fourths the length of the dish. 

 The motion of these copepods now became very slow; their 

 dorsal muscles were affected to such a degree that the swim- 

 ming feet could no longer beat with enough force to propel 

 them through the water. The mouth appendages also stopped 

 moving, and fifteen minutes later the copepods died. 



From these results it becomes evident that the chemicais 

 used have little effect on the behavior of the copepods to light. 

 In a few cases a reversal in the orientation was observable. 

 This was produced by the addition of hydrogen peroxide, mag- 

 nesium sulphate, nitric and acetic acids. In the last three 

 cases, however, the reversal may have only been incidental, for 

 but one or two of the copepods became negative while the 

 others remained positive. Generally those that did become 

 negative remained in this region but a short while, and soon 

 returned to the illuminated territory. In all the tests, when 

 the chemical reached the animals they became very active, as 

 if trying to get away from something that was affecting them 

 severely. But as the concentration of the medium was grad- 



