588 BRADLEY M. PATTEN 



reached the central point (fig. 1, 0). Then the starting light 

 was turned off and the lateral light thrown on, thus changing the 

 direction of the incident light through 90° without changing its 

 intensity. The course of a larva during this procedure was re- 

 corded by placing a drop of dilute methylene blue on its posterior 

 end and allowing the animal to trace its own trail on a sheet of 

 paper (fig. 1, P). Each larva was made to crawl through two 

 tests. One trail was begun under the influence of the starting 

 light near the observer, subjecting the maggot to the 90° change 

 in the direction of illumination from its right side, and one under 

 the influence of the starting light away from the observer, sub- 

 jecting the animal to a similar change from its left side. The 

 deflection of the trails was measured in degrees by means of a 

 protractor. The average deflection of the responses to right and 

 left stimulation was taken as an index of the sen"sitiveness of the 

 individual. 



The age of the maggots as given in the following records was 

 calculated from the time of their emergence as larvae. The eggs 

 were laid on the afternoon of August 26th, and the larvae hatched 

 early on the morning of the 28th. The 'first day' reaction- 

 measurements were made between 9 a.m. and 2 p.m. of the day 

 of hatching, and therefore represent the responses of animals 

 during the first day of larval life, rather than the responses of 

 larvae 24 hours old. Throughout the remainder of the experi- 

 ments, the measurements were made at the same time of day, 

 so the changes in reaction shown represent changes which have 

 taken place in 24 hour intervals. 



Since temperature affects their rate of development, a record 

 was kept of the temperature of the room in which the larvae were 

 raised (table 1). If larvae were reared under markedly different 

 temperature conditions, the maximum sensitiveness would be 

 likely to appear on a different day. It would in all probability, 

 however, be at the same relative age at which it was found in 

 these experiments. 



A group of 50 animals was isolated from a culture of Calliphora 

 Erythrocephala larvae, and this group divided into two parts: 

 (1) fifteen larvae each kept isolated in a separate culture jar so 



