iio Studies in Animal Behavior 



of substance involved and various external factors, 

 such as temperature and in some cases light. For 

 instance if alcohol is added to acetic acid one will 

 obtain ethyl acetate and water. On the other hand, 

 water added to ethyl acetate results in the forma- 

 tion of alcohol and acetic acid. The reaction in 

 either case does not proceed until all of the original 

 substances are transformed, but only to the point at 

 which certain proportions of alcohol, acetic acid, 

 ethyl acetate and water are reached. This repre- 

 sents the condition of chemical equilibrium. The 

 relative proportions of the compounds present when 

 chemical equilibrium is reached depend upon vari- 

 ous external factors. Sometimes one chemical change 

 may occur in the light, while the reverse process 

 takes place in the dark. Under the influence of 

 light the following reaction occurs : 



2AgCU Ag 2 Cl + Cl, 

 while in darkness there is the reverse change 



Ag 2 Cl -f Cl = 2AgCl. 



Many other compounds, especially the fulgorides > 

 show a similar reyersal under different intensities 

 of light. In certain cases chemical reactions are af- 

 fected in specific ways by the different rays of the 

 spectrum. 



"To explain," says Mast, "reversal in the sense of 

 reaction on the basis of chemical reactions induced 

 by light let us assume : ( I ) That Volvox contains 

 substances X and Y, the chemical reaction between 

 which is regulated by the intensity of light; (2) that 



