2 STUDIES IN GENERAL PHYSIOLOGY 
of a round plate covered with blue glass. The animals 
moved to the room side of the plate, tried to creep over the 
edge, and at 10:45 came to rest on the room side. I waited 
five minutes, and at 10:50 substituted red glass for the blue. 
The animals scattered equally over the whole plate, and at 
11 nine animals were on the window side, the rest about uni- 
formly scattered over the whole plate. I then substituted 
blue glass for the red. At 11:07 all the animals were col- 
lected on the room side of the plate. At 11:10 I again 
covered them with red glass. The animals immediately 
began to creep over the plate in all directions. At 11:20 
twelve animals were collected near the window, six in the 
middle, two on the side, and three on the room side of the 
plate. I kept the plate covered with red glass, and watched 
to see whether after a time the rays going through the red 
glass would not also bring about an orientation. No change 
occurred in the course of the next hour. Gradually, how- 
ever, more and more animals moved to the room side of the 
plate, and at 3:30 all but five animals were collected here. 
The animals, therefore, finally show a negative heliotropism 
under red glass also. The rays passing through red glass 
are therefore similar in their effects to those which go through 
blue glass, only they are not so effective. In this respect the 
behavior of these animals corresponds with that of plants. 
The larvee burrow into the ground. Negative heliotro- 
pism may co-operate here, but stereotropism is without doubt 
the chief factor concerned. 
The question arises whether it is not geotropism which 
causes the animals to bore into the ground, as in the case of 
roots. In order to determine this I made the following 
experiment: I filled a hollow cardboard cylinder, some 5 cm. 
in diameter, with earth. The cylinder was about 20 cm. 
high. I fastened the cylinder on a stand, with its longitudinal 
axis vertical, and brought it so near to a table that it 
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