30 A. M. REESE 



to collect in groups, in one place or another, without regard to 

 the light stimuli to which they are subjected; this tendency, 

 then, has no apparent bearing upon the following experiments. 



After hundreds of observations, extending over a period of 

 many months, upon several lots of animals, several sets of 

 observations were made upon one or two small groups of animals 

 immediately upon bringing them into the laboratory from their 

 native pond. Under these conditions the animals responded 

 either very indefinitely to the same light stimuli, or even in a 

 contrary manner to the animals that had been for some time 

 under observation. This irregularity in what had been con- 

 sidered the normal response was also noticed in a group of 

 animals that had been in the aquarium for a long time and had 

 not been used in the experiment for a considerable period. 



It is possible that, after all, the responses of the animals 

 under these abnormal conditions may be quite different from 

 what would be seen under normal conditions in their native 

 habitat. 



It is the intention of the author to carry on similar experi- 

 ments upon this species in the natural environment as soon as 

 a suitable spot can be found. (See Addendum.) 



Experiment I. — This experiment was to determine whether 

 Diemyctylus is positively or negatively phototropic towards 

 white light. 



Twelve animals were placed in the above-described aquarium 

 of water which was entirely surrounded by black except over 

 half of the top. Ten inches above the surface a 25-watt, 115- 

 volt tungsten lamp was so fixed as to illuminate exactly one- 

 half of the aquarium, the other half, of course, being thrown 

 in dense shadow. 



At regular intervals of five minutes the numbers of animals 

 in both light and dark ends were noted. When an animal, at 

 the moment of observation, happened to be partly in light and 

 partly in shadow it was counted for that region in which the 

 greater part of its length lay, though occasionally an animal 

 was so near the exact center that it was not counted on either 

 side. 



Table I shows that in 30 observations 95 animals were found 

 in the light and 250 in the dark. These observations were 



