REGULATION OF REACTIONS 297 



ants and various insects in their natural environment, one 

 can hardly fail to see that their reactions to light are any- 

 thing but fixed. Ants, for example, ordinarily avoid the 

 light. They are said to be negative. But they are not 

 always found in the dark recesses of their nests. Does 

 this mean that the sense of reaction changes? Light 

 undoubtedly guides them at times, and the sense of 

 reaction changes frequently, but sight no doubt plays a 

 part in the reactions. If a nest containing pupae or 

 larvae is opened, a given ant may often be seen, in caring 

 for the young, to travel back and forth repeatedly from 

 the brightest sunlight to the dark cavities of the nest. 

 Here it is evident that the ordinary negative response to 

 light has been modified. Again, the flight of bees from the 

 extreme darkness of the hive out into the brightest sun- 

 light, through shadow and sunshine, into and out of the 

 cavities of flowers and back into the darkness of the hive 

 again, offers another striking example of variability in 

 response to light, for it is no doubt light that guides these 

 organisms in many of their movements, although that in 

 which they are primarily interested is not light, but the 

 objects represented by different conditions or configurations 

 of light. 



We have thus seen that the reactions to light depend 

 upon various agents, and that they are modifiable and 

 variable to a certain degree in all organisms from the 

 lowest to the highest, i.e., that they are in general adap- 

 tive and regulatory. But in none of the lower forms 

 have such striking adaptive changes in reaction to light 

 been observed as Jennings records with reference to other 

 stimuli in his interesting description of the behavior of 

 Stentor and some other organisms (1906, pp. 170-179). 

 There is at present no greater need in the study of the 

 behavior of lower organisms than a comprehensive and 

 thorough quantitative study of the relative activity of 

 the different factors involved in regulation. 



