THE PHOTIC REACTIONS OF SARCOPHAGID FLIES 181 



cm.) on a triangular base. This vessel was then either filled with 

 pure water or a saturated aqueous solution of alum. Sunlight 

 was reflected on the prism by means of a small miror. The experi- 

 ments were carried on in a darkened room, usually with controls 

 and frequent repetitions. 



Experiment 5. July 27, 1907, 7.30 p.m. About 500 larvae 33 

 to 35 hours old were in a mass on the flesh. 



7 :52. The acetylene gas-lamp w^as placed in front of the box, 

 (12 to 14 cm. from the mass) causing the usual scattering of the 

 individuals toward the farther side of the box. In two minutes 

 the larvae were moving in a stieam toward the light, massing 

 directly in front of the flame. By 8:00 o'clock (8 minutes) all 

 but a few stragglers had collected on the glass front as high as the 

 flame. 



8:00. A red glass was placed in front of the lamp, resulting in 

 no apparent disturbance. 



8:05. The red glass was replaced gradually by a blue glass, 

 which also caused no noticeable disturbance. 



8:10. The larger number of larvae had crawled to the top of the 

 glass front, while the remainer had returned to the flesh. About 

 a dozen were found immediately opposite the flame, but these were 

 moving either up or down the glass front. 



8:15. The red glass was placed in position again. 



8.20. About half of the larvae had collected directly in front 

 of the light when the lamp was taken away leaving them in dark- 

 ness. 



8:35. The individuals had practically all returned to the flesh. 



9:15. After leaving the larvae in darkness almost an hour, the 

 lamp was once more placed in position with the blue glass. 



9:30. The animals, following the same tactics as before, had 

 crawled up the side of the box to the top (16 cm. of travelled dis- 

 tance from the flesh). 



Experiment 6. July 27, 1907, 2:20 p.m. About 500 larvae, 

 aged 28-30 hours, were contained in the glass box and massed on 

 the flesh. The light in this case was conducted through the prism 

 already described and used at a distance of three metres from its 

 source. Throwing the blue end of the spectrum on the mass 



