200 



WILLIAM BRODBECK HERMS 



tion under such circumstances brought the larvae into successively 

 higher intensities, and in consequence numerous trial movements 

 were produced and creeping ahead was accomplished very slowly. 

 As the larva advanced into regions of still higher intensities, its 

 trial movements were continued, though reduced in number, 

 but the rate of locomotion was increased. A very pronounced 

 change in behavior was evident when the point B was passed and 

 the path lay in light decreasing in intensity. The rate of movement 



Fig. 11 Outline of apparatus to produce a field of light increasing in intensity 

 in the direction of the rays. L, a 66 cp. incandescent lamp elevated on a stand (*S) ; 

 C, an opaque screen ; DD, an opaque screen with an oblong aperture about the size 

 of the incandescent bulb, to eliminate side light; AB, a field of light produced by 

 the lamp (L), gradually increasing in intensity from A to B. 



increased perceptibly, trial movements were visibly eliminated, 

 and the course was more nearly a straight line. The rate of move- 

 ment for a distance of 10 cm. on the brighter side of the point B 

 was greater by 10 per cent than for a like distance on the other 

 side of this point. This average is based on continuous movements 

 of ten larvae each given a single trial after 12 to 14 hours of re.-t. 

 In the field AB there was a very marked tendency on the part 

 of the larvae to take a diagonal course to the right or the left. 

 Out of 50 trials on 10 larvae, 50 per cent of the paths were diagonal, 



