HELIOTROPISM OF ANIMALS 11 
tions of the dish. When half of the vessel was covered 
with an opaque porcelain screen, Lubbock found 2,048 
animals collected under it, and 2,932 animals in the un- 
covered half. From these and similar experiments Lubbock 
concludes that the animals have a decided preference for 
yellow light. 
I also have made some experiments on the effects of 
rays of different refrangibility on Daphnia, and found that 
when the more refrangible rays (blue and violet) fell 
upon the animals they hastened to the source of light and 
moved up and down on the light side of the vessel. When 
I made the same experiment with the less refrangible rays, 
the effect was weak or did not take place at all. The result 
conforms with other facts which are to be described later. 
I shall, therefore, not revert to the Daphnia and their 
alleged ‘‘preference for yellow.” 
Lubbock has employed a similar method in his experi- 
ments on wingless ants;’ these, however, led to much more 
fruitful results than his experiments on Daphnia. In an 
experiment in which a vessel was covered with strips of 
red, green, yellow, and violet glass he found that 890 
animals collected under the red glass, 544 under the green, 
495 under the yellow, and only 5 under the violet. There 
is no doubt in this case that the animals collected under 
those glasses where they were struck by the less refrangible 
rays. Other experiments showed that red glass acts like an 
opaque body. 
The observation of Lubbock that ants avoid the ultra- 
violet part of the spectrum is also worthy of note. For the 
sake of completeness the experiments of Lubbock on bees 
and wasps must be mentioned, in which it was found that 
under otherwise similar conditions blue objects smeared with 
honey were preferred to those of another color. 
1 Luspock, “ Ameisen, Bienen und Wespen,” zbid., 1883. 
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