336 LIGHT AND THE BEHAVIOR OF ORGANISMS 



in the uncovered part of the dish there was at least as 

 much yellow light as under the yellow screen; or did the 

 majority 'hate' the blue light?" Referring to observa- 

 tions on Porthesia chrysorrhoea he says (1905, p. 29), 

 " This experiment shows that the more refrangible rays have 

 the same effect as mixed rays.'' 



The methods of both Lubbock and Wilson were how- 

 ever such as to leave little room for doubt regarding their 

 results. It is interesting to note that the recent work 

 of Stobbe (1908) on the photochemical changes in the 

 organic compounds known as fulgides demonstrates reac- 

 tions which proceed more rapidly in monochromatic light 

 of a given intensity than in the same light in combination 

 with other rays. These experiments have been referred to 

 under the section on photochemical reactions, p. 310. It is 

 likely that the chemical changes in Hydra and Daphnia 

 associated with their light reactions are of the nature of 

 certain fulgides. 



2. Bert's Experiments on Daphnia 



The first experiments dealing with the effect of differ- 

 ent colors on the reactions of multicellular animals were 

 made by Paul Bert in 1868. Bert was interested in 

 color vision. He attempted to answer the question as to 

 whether the specific effect on the different rays in the 

 spectrum is the same in the inferior animals as it is in 

 man. He attacked the problem from a purely psychologi- 

 cal point of view, as the title of his paper published in 

 1869 indicates: " Sur la question de savoir si tous les ani- 

 maux voient les memes rayons que nous." 



An electric-light spectrum was thrown on the flat side 

 of an aquarium covered with an opaque screen containing 

 a narrow vertical slit. Daphnias were exposed to the 

 different colors of the spectrum, and it was found that 

 they collected at the side of the aquarium nearest the 

 light, no matter which part of the spectrum was allowed 



