156 



H. C. STEVENS 



approximately 10x16x3 cms. The glass walls of the filter 

 were 5 mm. in thickness. Blue light was secured by an am- 

 moniacal solution of copper sulphate (10 gms. of copper sul- 

 phate to 300 cc. of water plus 10 cc. of ammonia). This solu- 



B/oe 



Yellow 



Figure 1 shows the reaction of Specimen 12 (VIII-25-1912, 12.30 P. M.) to blue 

 and yellow light. The head of the arrow indicates the head of the crab. The 

 dotted line indicates the path. The time spent in moving from (1) to (2) 

 was 25 seconds; from (2) to (3) 10 seconds. 



\A/h,re 



Yallow 



Figure 2 represents the reactions of the same crab as shown in Figure 1. The 

 time spent in moving from (1) to (2) was 30 seconds; from (2) to (3) 20 

 seconds. 



tion was placed in a filter similar in form to that which con- 

 tained the solution of potassium dichromate. The tops of both 

 filters were covered with a glass plate and sealed with balsam. 

 The color analyses and the spectral transmission of the lights 

 as determined by the Bureau of Standards are here given: 



