320 Journal of Comparative Neurology and Psychology. 



and dropped back into the water without touching any other 

 part of the body. Soon all became negative without exception. 

 After a few minutes they began to cross to the positive side of 

 the dish one by one, and it was but a short time before every 

 individual was positive. When I returned after an absence of 

 an hour and a half all of the specimens were negative, although 

 the light to which they were exposed had increased in intensity. 

 Warm water was then added so as to bring the temperature of 

 the medium up to 30° C. Four of the specimens soon became 

 strongly positive. These were picked up by the breathing tube 

 and dropped back into the water ; all became markedly negative. 

 As specimens came over to the light side of the dish they were 

 picked up and dropped as before, with the result, in almost 

 every instance, of producing a marked temporary negative reac- 

 tion. The next morning at 10 o'clock all of the specimens in 

 this dish and in another that was beside it were swimming 

 towards the light. They were all picked up and dropped back 

 into the water when, without exception, they became negative. 

 Soon they began to come over to the positive side of the dish 

 and in about half an hour they were all positive again. They 

 were all picked up and dropped a second time. All but two 

 became negative. At 2:40 in the afternoon the specimens in 

 each dish were aggregated into a dense bunch at the negative 

 end. When stirred up some seemed positive and some nega- 

 tive, but their reactions were not decided. The temperature 

 of the water in one dish was increased to 32° C. when about 

 half of the specimens became positive in an unmistakable de- 

 gree. When picked up and dropped into the water they 

 quickly became negative. When they became positive again 

 they were handled under the water without taking them out ; 

 as soon as released they showed an unmistakable negative 

 reaction. 



I have tried handling positive specimens under water re- 

 peatedly. The effect is, in nearly all cases, to produce a change 

 in the sense of the phototactic response. 



The effect of contact and disturbance is very marked also 

 on specimens while out of the water. This as well as other 



