BEHAVIOR OF AMPHIPODS WITH RESPECT TO LIGHT. 213 



the animals to the side of the tank farthest away from the lamp. 

 Comparative figures which will be given later indicate at least 

 that ray direction may force the animals to the side farthest 

 from the lamp. Possibly the data as regards light intensity 

 vs. ray direction has been over-emphasized. 



We can base our conclusions definitely on the effect of the 

 direction of rays only upon reactions with the tank set in position 

 2. The standard for this experimental work is based therefore 

 both upon light intensity and direction of rays. 



II. Responses of Untreated Amphipods to Light Intensity 



AND TO Direction of Rays. 



Table I. shows the reactions of untreated amphipods when the 



tank was at right angles to the direction of Hght rays (position i). 



Not only are the three species compared but also the stock kept 



in the laboratory several weeks is compared with that freshly 



brought in. 



Table I. 



Untreated Amphipods. 

 Experimental Tank at Right Angles to Direction of Rays (Position i). 



+ indicates a positive reaction, cc an indifferent reaction, — a negative reaction. 



The strongest negative reaction to intensity is shown by the 

 Hyalella and Eucrangonyx species, 73 to 77 per cent. This 

 means that in the 150 half minute readings, e. g., Eucrangonyx 

 6 weeks stock, only 13 per cent, of the animals were found in the 

 area of intense light, 11 per cent, in the medium or dim light 

 and 76 per cent, in the dark area. Although 13 per cent, were 

 in the field of intense light at the time the readings were taken, 

 yet, in most instances, the stay in that area was but momentary. 

 If the animals in their "random movements" or "busy explora- 



