184 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



studying the reaction of large groups of larvae which were placed 

 therein. The conditions of light were modified either by using 

 screens of black paper over one side of the jars, or by placing the jars 

 on a black or a white background. (2) Glass tubes. These were 

 for the most part straight glass tubes sealed with glass at each end. 

 These varied in length from 18 to 40 centimeters, and in diameter 

 from 2 to 4 centimeters. Other tubes were Y-shaped and were 

 constructed of glass tubing 3 centimeters in diameter. The horns 

 were 8, the stem 10, centimeters in length. The straight variety of 

 tube was used in various ways to test both the photopathic and the 

 phototactic reactions, under different conditions of light, background, 

 etc. The Y-tubes were used for a similar purpose and also to test 

 the reaction to different intensities of light. In this case sometimes 

 colored glass plates of different intensities were laid over the horns, 

 and sometimes the horns were laid over backgrounds of black or 

 white. It was under the conditions last mentioned that some of the 

 relations of photopathy to phototaxis were best studied. (3) Wooden 

 boxes supplied with glass bottoms, glass slides, or glass ends. These 

 boxes were 12 by 6 by 6 inches, painted black on the inside, and fitted 

 with light-tight covers. 



They also were used for testing the photopathic and phototactic 

 reactions either separately or in combination. In the latter case the 

 glass-bottomed box was set up over a hollow tube or shaft, through 

 which the light was reflected from a mirror, or from a plane, white 

 surface at the bottom of the shaft. Just beneath the glass bottom 

 of the box was ranged a linear series of monochromatic glass plates, — 

 red, orange, green, and blue, by means of which the intensity of light 

 entering the bottom of the box could be regulated. But light could 

 also enter the box through the end windows, and pass through the 

 box lengthwise. By this arrangement the larvae, when they were 

 placed in the box, could be subjected to two light influences: One 

 the light from below ; the other, the horizontal rays entering the end 

 window of the box. By these conditions of experiment it was 

 possible to secure reactions both to the intensity and to the directive 



