512 WILLIAM L. DOLLEY, JR. 



last 75 cm. and 12 also moved slower in the first part of the course 

 than in the middle of it. Moreover, the average rates in the 

 three portions of the course of the five animals tested in the 

 light ranging from 1.56 m.c. to 0.40 m.c. were, respectively, 

 2.779, 2.683, and 2.649 cm. per second, while the average rates 

 in the stronger light were, respectively, 3.173, 2.806, and 2.103 

 cm. per second. These results show that the butterflies tend 

 to move slightly slower as they come nearer the light, i.e., as the 

 illumination increases. 



Mast ('11, p. 186) obtained similar results in experiments on 

 the relation between the rate of movement and intensity of light. 

 He showed that fly larvae which crawled at the rate of 0.321 cm. 

 per second in a luminous intensity of 7 m.c. crawled at a rate of 

 0.345 cm. per second in an illumination of 3888 m.c. Thus, they 

 moved only 0.024 cm. per second faster in the very strong light 

 than they did in the weak light. It is evident that all of these 

 results militate strongly against the "continuous action theory" 

 of orientation. 



Table 2 also shows another interesting fact, namely, that 

 after the butterflies have traversed a few centimeters they tend 

 to move at a somewhat faster rate. Out of the 14 insects tested 

 in both sunlight and in weak light, 10 moved faster in sunlight 

 in the middle 75 cm. than in the last 75 cm., while in weak light 

 11 butterflies moved faster in the middle of the course than in 

 the last part of it. This phenomenon is very probably analogous 

 to the phenomenon of 'treppe' seen in stimulated isolated muscles 

 and in increased efficiency in athletes due to 'warming up.' 



BEHAVIOR IN INTERMITTENT LIGHT 



The results obtained in the experiments now to be described 

 present some evidence in favor of the theory that orientation 

 depends upon the time rate of change of intensity. This evi- 

 dence consists in the fact that Vanessa seems to move faster 

 when exposed to intermittent Hght of a certain frequency of 

 interruption than when exposed to continuous light. 



The method used in ascertaining this was as follows. A 

 circular disc of black cardboard fastened to a wheel and turned 



