THE PHOTIC REACTIONS OF SARCOPHAGID FLIES 191 



Table 3 shows clearly that the larvae grow more and more sensi- 

 tive to directive light and that they are perfectly negative when 

 the feeding period has ended. 



The newly hatched larvae appeared to be indifferent to the 

 direction of the rays, but an exposure of three minutes to a high 

 intensity (336 CM.) showed quite conclusively that even these 

 young larvae were negatively influenced by directive light. 



The imagoes emerge in a positive state. The small percentage of 

 negative reactions is based on a single reaction of one individual 

 whose wings were not spread, hence this behavior should be re- 

 garded as accidental. 



A record of the individual larvae is given in table 4 and is 

 serviceable in locating irregularities, e.g., the readings of Decem- 

 ber 14 and 16. These aberrant reactions are based on one indi- 

 vidual (no. 8), which proved to be very ''excitable" under me- 

 chanical stimulation; thus, a slight pressure or dropping carelessly 

 caused the larva to start moving at once without first orienting 

 itself to the light. This table also shows that there is no di er- 

 ence between the reactions of the males and of the females to 

 light. 



4. Reactiveness and intensity 



Even the casual observer must be familiar with the general 

 negative reaction of the migrated fly-larvae, observable through a 

 considerable range of intensities, i.e., to bright sunshine, to diffuse 

 dayhght, and to ordinary lampHght. It has already been pointed 

 out that the migrated larvae of Ijucilia caesar are uniformly 

 negative to directive incandescent lampHght of 0.56 CM. intensity. 

 It remains to be seen what the degree of sensitiveness is at lower 

 intensities. Since the reaction of the migrated larvae is quite 

 uniform, the series of experiments with reference to sensitiveness 

 was made during the prepupal period. The methods described 

 in section 3 for larvae at this period were likewise applied in this 

 case, as was also the low-intensity box with the diaphragms 

 Usted in table 2. The individual was placed in Square E6 (the 

 central square of the reading frame, fig. 1, E), the dark cham- 

 ber (B) was closed, and after the lapse of thirty seconds the posi- 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 10, NO. 2 



