184 WILLIAM BRODBECK HERMS 



out of range in a few minutes, excepting a few (6) which were 

 crawHng about at random in the blue and green. 



2:45. No change of position on the part of the aggregated lar- 

 vae had taken place. (The migrated individuals come to rest 

 usually in a mass, when retained in a receptacle, making few move- 

 ments during the day, except in response to changes in light. Con- 

 sequently it was a comparatively simple matter to make observa- 

 tions.) By gradually moving the mirror it was possible to keep 

 the mass of larvae moving under the blue and violet, thus driving 

 them out of a corner and across the glass side of the box, however 

 slowly. This reaction could not be secured by means of the red 

 and yellow. The observations were carried on until 3 :30 p.m. 



III. THE INDIVIDUAL LARVAE AND ADULTS 



1. Introduction 



That the positive reaction to light as described in the last 

 section is not the usual reaction of the single larva, is evidenced 

 by the fact that the individual invariably goes away from the 

 source of light. It has already been intimated that the older lar- 

 vae are more strongly negative to light than the younger individ- 

 uals. It is quite generally known that the adult flies are positive 

 to light, i.e., fly toward the source of light. Hence, it is evident 

 that the sarcophagids form a group of organisms whose reactions 

 show progressive change; viz. first, during the feeding period 

 the larvae as an aggregation of individuals react positively to 

 artificial light though as individuals they are apparently strongly 

 negative; secondly, the migrated larvae (in the prepupal period) 

 are uniformily negative; and, finally, though the larvae pupate 

 as negative organisms they emerge in a positive state. 



It is clear that a series of experiments is needed on a number 

 of individuals throughout their life history, at definite intervals 

 and at a given light intensity, in order to determine the degree of 

 reactiveness for the various periods, or stages. Further, the range 

 of intensity through which the individuals react should be con- 

 sidered and determined. It has been shown in the earthworm 

 (Parker and Arkin, '01) that there is a localization of the light 

 receptive function; it is also quite likely that this function is 



