THE PHOTIC REACTIONS OF SARCOPHAGID FLIES 177 



ments of the larvae, especially at this stage. Here they collect, 

 not always in one mass, but usually so. While certain experiments 

 were being carried on it was noticed that the larvae responded 

 very definitely to ordinary lamplight. This particular response 

 was not negative but positive; that is the larvae left the flesh 

 upon which they were feeding and moved toward the light, taking 

 up a position finally at a point as near as possible to the source of 

 light. This peculiar reaction was first observed on the evening of 

 June 30, 1905, and is more fully described as follows: 



Experiment 1. June 30, 1905. This was an experiment on 

 larvae of Lucilia caesar, which under experimental conditions had 

 crawled into a small vial 12.7 cm. in length, containing a piece of 

 fish weighing about one gram. Within ten minutes after lighting 

 the lamp the larvae, (between sixteen and eighteen hours old), 

 numbering thirty-six, were noticed to leave the flesh, crawling 

 rapidly toward that part of the vial nearest the light. This took 

 them 4.5 cm. away from the food; changing the angle between the 

 vial and the light, or rolling the vial over always resulted in a 

 readjustment on the part of the individual animals. Moving 

 the lamp from one side of the vial to the other likewise resulted in 

 readjustment. Gradually increasing the distance between the vial 

 and the light resulted in a final return to the food when a maximum 

 of four metres was reached. On bringing the lamp near again, the 

 larvae once more left the meat when the light was three metres 

 distant. The experiment was repreated several times with like 

 results, not only with the same larvae, but with different sets of 

 individuals. 



The experiment was tried one year later with the following 

 results, which are practically identical with the results of Experi- 

 ment 1. 



Experiment 2. July 24, 1906, 8:20 p.m. A covered glass vessel 

 (containing larvae feeding on fish) was placed in position on a 

 table with a lamp 40 cm. distant. 



8:30. The larvae were moving away from the flesh. 



8:35. They had collected at the point within the vessel which 

 was nearest to the light, at a distance of 2 to 5.2 cm. from the flesh. 



