204 WILLIAM BRODBECK HERMS 



Davenport and Cannon found that the relation existing between 

 the rate of movement (Daphnia) and the intensity of the light 

 could be expressed thus: with one-fourth light, about 118 percent 

 of the time with full light. Yerkes expressed this in the following 

 ratios: ratio of intensities 5.12: 1, and ratio of rates 1:1.25. By 

 calculation such ratios may be roughlj^ approximated in table 

 6, however, only with regard to the higher intensities. No like 

 ratios could be established for the light of lower intensities, since 

 under such conditions the course of the larvae is not continuous, 

 but is greatly influenced by random movements. It must also 

 be noted that the maximum rate for any single larva (1.64 second 

 per cm.) was already attained in the 1057 CM. intensity by one 

 individual and not exceeded in 5000 CM., though the average for 

 this intensity is 1.88 sec. per cm. (See also Nutting, '08, in this 

 connection.) 



It is apparent that the rates for the two species are quite differ- 

 ent, but the ratios hold approximately for each. It was quite 

 out of the question to secure a set of even approximately uniform 

 rates in low intensities for C vomitoria, because of the extreme 

 individual variation, due to hesitation and wandering. 



7. Sudden change in intensity 



One is naturally led to ask the question: What is the natur? of 

 the response when a light is thrown suddenly from above upon the 

 animal as it creeps in the dark or in an illumination of low intensity. 

 If one considers for a moment what the result would be upon an 

 animal having eyes, one might be led to expect a similar result 

 under similar conditions when a fly-larvae is suddenly illuminated, 

 viz. that it would pause momentarily, at least, and probably be 

 thrown out of orientation. But it must be considered that in 

 the sarcophagid larva we have to deal with an eyeless organ- 

 ism. Various observers have found that certain organisms 

 are thus affected to a greater or less degree. Yerkes ('00, pp. 

 416-417) found that neither Daphnia nor Cypris responded by 

 turning, but that both species quickened their movements as 

 the result of sudden illumination from above. Jennings ('04, 



