REACTIONS OF ARTHROPODS TO LIGHTS 469 



by means of screens, unless the different colors are made equal 

 in intensity. 



Many investigators have ignored the important factor of 

 intensity and ha\-e ascribed the effect of colored lights on the 

 organism as due solely to the quality of the light. Others have 

 recognized the importance of intensity, but as far as I know the 

 only experiments on animals in which this difficulty has been 

 successfully overcome are those described in two very recent 

 papers pubhshed b}' Day ('11) and Laurens ('11). These two 

 investigators measured accurately the intensity of monochro- 

 matic spectral lights by means of an extremely dehcate instru- 

 ment, the radio-micrometer of Bo,ys. This apparatus has opened 

 the way to the correct solution of many interesting problems 

 involving the reactions of animals to colored lights, investigations 

 which heretofore have yielded so many conflicting and perhaps 

 questionable results. 



This present investigation was taken up at the suggestion of 

 Prof. G. H. Parker and whatever success has been attained is 

 due to his untiring interest and helpful criticism throughout the 

 whole course of the work. I am also indebted to Dr. H. Laurens 

 for cooperation in the construction of the light generators used 

 in the experiments. 



2. HISTORICAL 



Much of the earlier work on the reactions of arthropods to 

 colored lights was taken up from a purely psychological point 

 of view. The investigators seem to have worked with the sole 

 purpose of answering the question of whether the lower animals 

 are able to perceive colors as such and, if so, do they perceive 

 the same colors of the spectrum as seen by the normal human 

 eye. 



The first recorded experiments, to my knowledge, upon the 

 reactions of the arthropods to colored lights are those of Paul 

 Bert who published an account of his work on Daphnia in 1868. 

 He discovered that the Daphnia responded to each of the visible 

 colors of the spectrum. When the entire spectrum was thrown 



