220 BRADLEY M. PATTEN 



It is interesting that in the imago the conditions are reversed, 

 and the blue is more effective than the green. 



In the work which has been done on the Hght reactions of the 

 blowfly larva there is essential agreement as to the general man- 

 ner in which the animal actually behaves under various experi- 

 mental conditions. The interest of recent work has centered 

 about the discussion of details of behavior which have been 

 adduced in support of one or the other of the theories of orien- 

 tation. There has been no attempt made to obtain definite 

 measurements of any phase of the orienting reaction. The pur- 

 pose of the present paper is to devise a method of quantitative 

 measurement which shall be available in work on light reactions 

 and to apply such a method to the orienting reaction of the 

 blowfly larva. 



APPARATUS 



The apparatus used in these experiments was constructed so 

 that the opposite sides of the animal under observation could be 

 subjected to opposed beams of light the actual and relative 

 intensity of which could be varied at will. The plan of the 

 apparatus is shown in figure 1. 



It consisted of a horizontal wooden frame in the form of an 

 isosceles right triangle. As shown by the dotted lines on the 

 diagram, this frame was so proportioned that a similar triangle 

 measuring two meters on the base and 1.414 meters on the equal 

 legs, could be laid out on it. Where the side bars of the frame 

 came together to form a right angle, a horizontal platform 65 by 

 35 cm. was attached. On this platform, at the apex of the 

 triangle were set up five 220-volt Nernst glowers, mounted 

 vertically and about 5 mm. apart, each with a switch in circuit. 

 Their position was such that no glower interfered with the light 

 thrown on the mirrors by any other glower. When less than the 

 five-glower intensity was desired, symmetrically placed glowers 

 were used. 



A portion of the light from these glowers passed through the 

 horizontal rectangular apertures (3.2 by 6.1 cm.) in the screens 

 d and d', placed 25 cm. from the glowers. 



