GERTRUDE MAREAN WHITE. 



The larvae were placed in a small square glass container 

 (5 cm. x 5 cm. x 2.5 cm.) ; opposite one side was placed a lo-watt 

 Mazda lamp in a light-tight box (5.5 cm. x 5.5 cm. x 9 cm.) with 

 an opening on the side toward the aquarium. The opening was 

 covered by a smoked glass which reduced the illumination to 4.4 

 candle power. This box was movable on a meter scale toward 

 and away from the container. Opposite an adjoining side of the 

 aquarium at right angles to this was another box (5 cm. x 5 cm. x 

 14 cm.) containing a 15-watt Mazda candelabra lamp, in front of 



Sc 



M 



{ p 



FIG. i. Diagram of apparatus. A, aquarium; F, Wratten light filter; M, 

 movable lamp; Me, meter stick; P, removable partition; 5, stationary lamp; 

 Sc, opaque screens. 



which could be inserted monochromatic light niters; this box 

 was in a fixed position with the light 10 centimeters from the 

 aquarium. Both lamps were operated by a single switch so that 

 the larvae could be exposed simultaneously to light from the two 

 sources. The lamp producing white light was moved back and 

 forth on the meter scale until the point was found at which the 

 larvae distributed themselves equally with respect to the two 

 sources of light. The white and the colored lights were then 

 considered to be of equal stimulating effect. Black screens with 

 openings somewhat larger than the source of light were so 

 arranged as to minimize reflected light (Fig. i). 



