376 



S. O. MAST 



the colonies began to scatter, evidently becoming neutral again. 

 Thus they remained for some time, then they became negative, 

 and finally collected along the side of the aquarium farthest 

 from the source of light as definitely as they had formerly col- 

 lected on the opposite side. This again occurred first in the 

 highest and last in the lowest illumination. 



In all of the aquaria the smaller colonies invariably became 

 negative before the larger ones. Thus there was often found in 



TABLE 1 



Relation between time of exposure, intensity of illumination and reversion in 



orientation 



aquaria a very definite positive collection and at the same time 

 an equally definite negative collection. Later, however, prac- 

 tically all of the colonies became negative, and the record in the 

 table indicates the time when this occurred in each aquarium. 



The table mentioned contains the results obtained in two ex- 

 periments made on two successive days with the same organisms. 

 By referring to this table it will be seen at once that reversion 

 from positive to negative orientation depends upon the intensity 

 of illumination and upon the time of exposure, but that the energy 



