ABSTRACT
Experiments were carried out with Daphnia to see whether the phototropism and galvanotropism which they exhibit would, when the animals were exposed simultaneously to light and to electric current at right angles to each other, induce a resultant reaction such as occurs in many phototropic animals when exposed to two sources of light simultaneously.
Considering the rather difficult nature of the material (consequent on the number of small specimens present, the prevalence of quiescence or inhibition, and the all too frequent modifiability and variability of behaviour among some individuals in the cultures), the following results may, I think, be seen sufficiently clearly: A resultant reaction in the large specimens, doubtfully in the small ones; positivation, by the current, of the photonegative large specimens, but not of the small animals ; kathodic galvanotropism in the large, but not in the small individuals. The threshold value of the current, for galvanotropic reaction alone, and for resultant reaction and positivation, has been found; and finally the latter threshold value has been shown to be independent of the light intensity. The current threshold for resultant reaction, with the light intensities tried, is seen to be the same as that for kathodic galvanotropism alone.
