52 



NATHAN FASTEN 



The chemical experiments were all performed at night, when 

 the only source of illumination was a 60 c. p. Mazda globe sta- 

 tioned about a foot from the receptacle containing the cope- 

 pods. Most of them were also confirmed in diffuse day-light. 

 The observations were made in oblong glass dishes whose dimen- 

 sions were eight inches long, one and one-fourth inch wide, 

 and one and one-fourth inch high. The number of copepods 

 used in each case was four or more. 



Before applying a reagent, the copepods were first attracted 

 to one end of the dish and then the chemical was slowly poured, 

 drop by drop into the opposite end of the vessel. The following 

 table gives a condensed statement of the results obtained. The 

 sign + is used whenever the copepods reacted positively to 

 light, whereas the sign — is used when the reaction to light 

 was negative. 



Lowest percentage 



of chemical Time required to Behavior to light 

 Chemical used causing death kill copepod until death 



Sodium chloride 1.2 15 min. + 



Potassium chlorate 0.2 4 " + 



Calcium chloride . 85 4 " + 



Hydrochloric acid .OS 2 " + 



Sulphuric acid 0.015 3 " + 



Tartaric acid .45 2 " + 



Oxalic acid 0.3 2 " + 



Copper sulphate 0.2 5 " + 



Acetic acid. 0.1 3 " f (indication of 



reversal) 



Nitric acid .03 16 " + (indication of 



reversal) 



Magnesium sulphate 1.6 45 " 2 +, 2 — 



Hydrogen peroxide 9.0 18 " — 



Copper sulphate was found to affect the copepods differently 

 during the day than at night. In the dark room a solution of 

 0.2 per cent copper sulphate caused all the copepods to die in 

 about five minutes. In daylight, however, a two per cent solu- 

 tion of the chemical affected the animals very little. After 

 remaining in this medium for twenty minutes they appeared to 

 be as active at the end of this time as at the beginning. When 

 the solution was increased to three per cent the organisms died 

 in about four minutes. Evidently these differences in the 

 behavior of the free swimming copepods depend upon differences 

 in their physiological states, which may perhaps have been due 

 to minute differences in the environment of the animals at the 



