214 BRADLEY M. PATTEN 



titative measurement of the light reactions, in some suitable and 

 easily available animal. The light was applied as two opposed 

 beams, the intensity of which could be easily controlled and 

 precisely measured. The responses to the stimulation produced 

 by two beams of different intensity acting simultaneously on 

 opposite sides of the same animal were measured in angular 

 deflections from an initial path of locomotion. 



LITERATURE 



The earliest paper on the light reactions of blowfly larvae was 

 that of Pouchet, in 1872. He described a series of experiments 

 with daylight and artificial light, showing the negative character 

 of the light response of the larvae of several species of the old 

 Linnaean family of Muscidae. A considerable portion of the 

 paper is devoted to experiments devised to locate the light 

 recipient organs. The fact that the light response did not dis- 

 appear when the sensory cones of the anterior end were excised, 

 led Pouchet to conclude that the imaginal discs of the adult 

 compound eyes were the sensitive organs. This conclusion was 

 borne out by his observations on the increase of sensitiveness 

 with the age of the larva, which coincides with the increase in 

 development of the imaginal discs. .The following quotation 

 sets forth his interpretation of the way in which the imaginal 

 discs serve, not only to perceive the light but also the direction 

 of the rays (1872, p. 316) : "La lumiere, frappant, sous des angles 

 different, les surfaces toutes different inclinees sur I'horizon des 

 yeux embryonnaires, donne a Tanimal le sentiment de la direc- 

 tion des rayons, par I'intensite relative avec laquelle ils affectent, 

 grace a leur incidence, les different yeux." 



This conclusion is interesting in its foreshadowing of the ques- 

 tion of the relative effect of 'ray direction' and 'intensity differ- 

 ence' on orientation which grew out of the tropism controversy 

 nearly twenty years later. 



The work of Pouchet, like most studies of behavior of this 

 period was done on the basis of preference as shown by experi- 

 menting. Conditions were so arranged that the animals could 

 move into regions of higher or lower intensity or of particular 



