QUANTITATIVE DETERMINATION OF LIGHT REACTIONS 219 



nation, the positive reaction of aggregations of feeding larvae 

 to a light of moderate intensity, and the circus movements per- 

 formed by larvae with one side of the anterior end blackened. A 

 valuable part of the paper is occupied with the confirmation by 

 more exact experimental data, of several of the earlier conclusions. 



Mast in his extensive treatise on 'Xight and the behavior of 

 organisms" has collected practically all the important work of 

 the earlier writers and added many experiments of his own. His 

 original work is similar to that of Jennings in the careful obser- 

 vation of the details of individual behavior. One cannot fail to 

 be impressed by the painstaking methods of his experiments, 

 but it is difficult to see how his results invalidate the theories of 

 Loeb so completely as he would have us believe. 



Considerable space is devoted to the reactions of fly larvae. 

 Experiments are described which bear out the conclusion of Loeb 

 and Herms that the sensitive region is restricted to the anterior 

 end, but none of them aid materially a precise localization of the 

 sensitive organs. His experiments on the effect of intensity 

 on the rate of locomotion failed to yield any very definite results, 

 largely because they were made with horizontal lights and hence 

 the shadow of the animal's body prevented the direct operation 

 of the light on the sensitive anterior end. The most interesting 

 part of his work is the series of experiments by which he estab- 

 lishes that, in this form as well as others on which he worked, ori- 

 entation depends primarily on the intensity which operates on the 

 sensitive surfaces, but depends on 'ray direction' only in so far as 

 it modifies the operative intensity on the receptive areas. His 

 analysis of orientation will be taken up in same detail in the 

 discussion of theories of orientation. 



Several authors have experimented with the effect of colored 

 light on maggots, but the work of Gross ('13) is, by reason of the 

 refinements of his apparatus and methods, by far the most ac- 

 curate that has been done is this field. The colors used in his 

 experiments were practically monochromatic and were accurately 

 measured for intensity by means of a radiomicrometer. The 

 sequence of effectiveness which he established for the larvae- 

 green, blue, yellow, red, decreasing in the order named — is 

 unusual in the greater effectiveness of the green than the blue. 



