338 LIGHT AND THE BEHAVIOR OF ORGANISMS 



Journal of the Linnean Society in 1881. The following 

 account is however taken from a later publication (1882, 

 pp. 212-231). 



In these experiments Lubbock projected a prismatic 

 solar spectrum arranged by Professor Dewar at the Royal 

 Institute, vertically downward on a wooden trough 14 

 inches long and 4 inches wide. In this trough he put 

 50 specimens of Daphnia pulex, scattered them equally 

 through the water, and after ten minutes inserted glass 

 partitions so as to divide the trough into compartments 

 corresponding in size with the five principal colors of the 

 spectrum. He then recorded the number of individuals in 

 each, after which he repeated the process. The total for 

 ten trials follows: 5 in the violet, 32 in the blue, 298 in 

 the green, 74 in the yellow, 90 in the red and one in the 

 dark part of the spectrum. 



In comparing these results it is necessary to consider 

 the fact that in a prismatic spectrum the red and green 

 are each much more than twice as wide as the yellow; and 

 the blue and violet are each wider than the green. Lub- 

 bock allowed three-fourths of an inch for the yellow and 

 two inches for the green. Correcting for this difference 

 in width the calculated number in the yellow would have 

 been 196. Lubbock concludes (p. 214), "It will be 

 observed . . . [that] there were more Daphnias in pro- 

 portion, as well as absolutely, in the green, although the 

 yellow is the brightest portion of the spectrum." 



It was also found that when daphnias were exposed in 

 the green, yellow and red of a normal spectrum, they col- 

 lected in the green rather than in the red. In these experi- 

 ments the region of highest intensity in the middle of the 

 field was shaded. After ten minutes' exposure 410 speci- 

 mens were found in the green end, 14 in the shaded area 

 and 76 in the red. These results indicate clearly that if 

 brightness alone controls the reactions of Daphnia, it 

 must be different for them than it is for the human eye. 

 Numerous convincing experimental results showing that 



