272 STUDIES IN GENERAL PHYSIOLOGY 



hand to show that the phenomena of the liberation of energy 

 produced by the light show different characteristics in posi- 

 tively and negatively heliotropic animals to correspond with 

 this theory. Negatively as well as positively heliotropic 

 animals execute progressive movements under the influence 

 of light, independently of their orientation, and a difference 

 could be expected only in the efforts which the animal must 

 make to execute the given progressive movements. It might 

 be thought that in positively heliotropic animals light brings 

 about a condition of the muscles or the nervous system in 

 which the liberation of energy is made easier, while in nega- 

 tively heliotropic animals a condition of the muscles is 

 brought about by the light in which the liberation of energy 

 is made more difficult. I have given some observations in 

 sec. 4 of this paper which seem to sustain such an assumption. 

 Before doing this, however, I wish to acquaint the reader with 

 a series of new facts which deal with the transformation of 

 positive heliotropism into negative, and vice versa. 



III. ON THE TRANSFORMATION OF POSITIVE HELIOTROPISM 

 INTO NEGATIVE HELIOTROPISM, AND THE REVERSE 



1. In my earlier papers I was able to describe such ani- 

 mals only as were constantly positively or negatively helio- 

 tropic. Later, Groom and I described some observations at 

 Naples on the behavior of the nauplii of Balanus perforatus, 

 and certain other marine animals, which were at times nega- 

 tively heliotropic, and at other times positively heliotropic. 1 

 We found that the intensity of the light determines the sense 

 of heliotropism in these animals. Above a certain intensity 

 light makes these animals negatively heliotropic, and this 

 the more quickly the greater the intensity of the light. 

 By lamplight the animals were always positively heliotropic. 



I have made further experiments on pelagic animals at 



i"Der Heliotropismus der Nauplien von Balanus perforatus," Biologisches 

 Centralblatt, Vol. X. 



