THE BEHAVIOR OF A PARASITIC COPEPOD 53 



times when they were secured; perhaps the individuals used 

 during the day were younger, and therefore possessed greater 

 vitality. 



In acetic acid, nitric acid, magnesium sulphate and hydrogen 

 peroxide the copepods gave indications of reversal in their 

 behavior to light. 



Acetic acid. — Acetic acid was slowly added until the water 

 became a o.i per cent solution of the chemical. As the acid 

 reached the copepods they became very active. One of them 

 circled clear across the dish from the side nearest the light to 

 the opposite end. The next moment, however, it moved into 

 the light again, where it remained till death. In three minutes 

 all of the. copepods died in the illuminated region. 



Nitric acid. — This chemical was slowly added to a dish of 

 water containing four copepods. When the medium became a 

 0.03 per cent solution, the animals became very active, darting 

 rapidly about in the light for nearly ten minutes. Then two of 

 them died, while the other two moved a little towards the oppo- 

 site side. The latter reaction was but momentary, however, and 

 the copepods again returned to the illuminated region. One 

 now began to move away from the lighted side, but when it 

 traveled about one-third the distance it returned into it again 

 and remained there till death. No actual reversal took place 

 although there were very strong indications of the organisms 

 trying to avoid the chemical. 



Magnesium sulphate. — These observations lasted from 8.22 

 P. M. to 9.10 P. M. When the magnesium sulphate was added 

 to the water gradually, the copepods remained positive until 

 the concentration reached one per cent. Here the addition of 

 the chemical was suspended, and after a wait of a few moments, 

 one copepod was seen making its way from the lighted region, 

 while the others kept moving about within it. When a card 

 was suddenly flashed between the dish and the light, the pass- 

 ing shadow caused the negative copepod immediately to become 

 positive again. When more magnesium sulphate was added 

 until the solution was 1.6 per cent, two copepods died, while 

 the other two became negative. Passing a shadow between the 

 light and the dish brought them back again into the positive 

 region, but as soon as this ceased, they again became negative. 



