490 ALFRED O. GROSS 



In the reverse of this pair, yellow-green, the number 21 in the 

 column headed by yellow and in the line faced by green indicates 

 that 21 per cent of the flies used went to the yellow. In a like 

 manner the results obtained with any pair of lights may be 

 readily ascertained. 



From the above series of records it is at once apparent that 

 the adult blow-flies are responsive to all the colors, and, of the 

 lights used in these experiments, are affected most by those 

 containing the more refrangible rays. The effectiveness of the 

 colors in stimulating Calliphora, therefore, are in order, begin- 

 ning with the strongest: blue, green, yellow, red. 



C. Drosophila ampelophila Loew (adult) 



The pomace or little fruit fly, Drosophila ampelophila Loew, 

 is a very common insect for experimental work, not on light 

 alone, but in a great diversity of lines of investigation, because 

 of the ease with which vast numbers can be reared and handled 

 in the laboratory. Carpenter ('05) has demonstrated the strong 

 positive reaction of Drosophila in its response to white light, 

 but no one, as far as I am able to discover, has made careful 

 investigations of the reactions of these insects to monochromatic 

 light. The tests made with Drosophila in the following investi- 

 gations were carried out in practically the same way as those 

 made with the adult blow-fly. Since the pomace fly is so closely 

 related to the adult blow-fly and has the same type of visual 

 mechanism as that insect, one would naturally expect in experi- 

 ments with it to obtain results similar to those from the blow- 

 fly. 



1. Material. A continuous culture of Drosophila derived from 

 an original stock secured during the summer was maintained 

 in the laboratory throughout the winter. They were reared in 

 large glass jars which contained a supply of decaying bananas 

 on which the insects fed and deposited their eggs. By inverting 

 a large glass funnel over such a culture and directing it upwards 

 and towards a strong light the flies can, because of their strong 

 reactions, be easily conducted through the funnel into small jars. 



