2 - 



FERNANDUS PAYNE. 



introduced into this tube by means of a shell vial three and one 

 half inches in length and large enough to slick' over the end of 

 the glas> tube. The end and about one half inch of the side of 

 this vial were also covered with black cloth so when the vial was 

 slipped over the tube, the tube admitted no light except at the 

 end toward the lamp. By means of a stop watch I obtained tin- 

 time it took each fly to travel the distance of nine and three 

 eighths inches toward the light. Someiimes the flies did not 

 react and in such cases they were counted out at the end of one 

 minute. Records of these flies were also kept. This limit 

 wa> placed at one minute, as experience showed that if they did 

 not react within this time they might not react for five or ten 



B 



FIG. I. Arrangement of the apparatus. A, the shell vial, three and one half 

 nches in length; B, the glass tube, nine and three eighths inehc< IHUL;; C, the heat 

 screen, three inches thick; D, the light, ten and three fourths inches from the end 

 of the glass tube. The parts colored black wen? wrapped with black cloth. 



minutes, or even longer. Extreme care was used to have ex- 

 ternal conditions as nearly uniform as possible. The temperature 

 of the room at the time of testing varied between 74 and 78 

 degrees Fahr., but I could not see that a variation within this 

 range made any difference. All flies were changed to perfectly 

 clean vials and allowed to Mand from ten to thirty minutes before 

 testing, so they might become accustomed to a clean surface 

 such as the inner surface of the tube into \\ Inch they \\eiv intro- 

 duced. The flies bred in the dark \\ere placed in the light during 

 this ten to thirty mimito in onlrr to overcome any temporary 

 effect of the darkness. All tlirs \\ere tested at approximately 

 the same age, from six lo twenty-lour hours alter hatching. 

 They were fed on ban. ma which wa^ penniiied \o reach about 

 the same degree of fermentation before using. 



