72 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 ajbout 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 larvse 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 



