FURTHER INVESTIGATIONS ON HELIOTROPISM 93 



Within the next few days the six first-mentioned animals 

 further elevated their heads, so that the animals on Decem- 

 ber 22 eight days after being placed in the aquarium 

 were all similarly oriented toward the light. The head was 

 directed toward the window, and the axis of symmetry of 

 the gills which were exposed to the light lay in the direction 

 of the more intense rays of daylight which entered from 



FIG. 8 



without and above. I waited to discover whether this orien- 

 tation would last. The aquarium remained undisturbed 

 until February 16, 1890 ; that is, for more than two months. 

 The animals also did not change their positions, as indicated 

 in Fig. 7. 



3. On the afternoon of February 17, 1890, the aquarium 

 was turned 180 about its vertical axis, and the zinc box 

 was again inverted over the aquarium so that the movable 

 end was directed toward the window. By turning the 

 aquarium around in this way, the heads of the animals, 

 which had been until then directed toward the source of 

 light, were suddenly turned toward the room side of the 



