256 BRADLEY M. PATTEN 



lamps was enclosed in a case, light proof, except for a diaphragm 

 3 by 3 cm. The diaphragms were placed so that the central 

 ray of the beam transmitted was directed toward the center of 

 the observation circle. Determinations of the illumination de- 

 livered by the lights were made with standard candles and a 

 Bunsen photometer. Each fixed light gave, at the center of 

 the observation circle, an illumination of 120 candle meters. 

 The intensity of the third light was varied by moving it to dif- 

 ferent positions along the axis. Records of its intensities are 

 given in connection wdth the experiments in which it was used. 

 The whole apparatus was located in a dark room and, in order 

 to reduce reflected light to a minimum, all parts of it except the 

 scales were painted flat black. 



MEASUREMENTS OF REACTIONS TO LIGHT 



Eighteen normal and active specimens were available for the 

 experimental work. Identification numbers were painted on the 

 back of each animal so the records of the same individual might 

 be compared under various conditions. Nothing being known 

 as to the nature of their reactions to light, preliminary qualita- 

 tive observations were necessary. Each animal was therefore 

 started from the center of the observation circle first heading 

 directly toward the source of a single horizontal beam of Ught, 

 second heading away from the source of light, and, third, head- 

 ing across the beam of light. The animals without exception 

 moved away from the source of light. Furthermore, the turn- 

 ings although not always instantaneous, were always direct. 

 There was nothing which could possibly be construed as a 

 'trial movement'. The turning of uhexcited animals was a 

 deliberate, coordinated rotation of the body about the thorax 

 as a center. Turning was sometimes accompanied by locomo- 

 tion but often orientation was nearly completed before the 

 animal began to crawl. The center of rotation was between the 

 middle pair of the legs functional in walking (i.e., the third 

 pair of legs.) In turning, the anterior walking leg on the side 

 toward which the animal was swinging, pulled, while its fellow 

 on the opposite side pushed. The middle pair of walking legs 



