MULTICELLULAR ANIMALS AND COLOR 335 



to exclude from the aquarium all light excepting that 

 proceeding from the prism" (Footnote, p. 430). In the 

 spectrum, which was about three inches long, the hydras 

 showed a very marked tendency to collect in the lower 

 blue, from line G to line F, and for a slight distance in the 

 green. They were wholly indifferent to the lower rays, 

 the violet and ultra-violet, as well as to all those above the 

 lower green, including the infra-red. It should be empha- 

 sized that they are not negative in these colors. This was 

 shown both by their reactions in the spectrum and by 

 those under colored glass. 



The observations of Wilson seem to prove conclusively 

 that the blue is most active in stimulating both Hydra 

 viridis and Hydra fusca. This stimulating activity of the 

 blue is specific; it bears no definite relation to the distri- 

 bution of energy or of brightness, both of which are fairly 

 definitely located for the gas-light spectrum, the region of 

 maximum energy and brightness being well toward the 

 red end. 



One of the striking peculiarities in the results obtained 

 by Wilson is the fact that whereas hydras collected most 

 abundantly in the regions of highest intensity under given 

 color conditions, more were regularly found in the blue than 

 in daylight, when they were given a choice between these 

 two conditions of light (see Table XII), although the latter 

 contained at least as much blue as the former and was of 

 course more intense owing to the presence of other rays. 

 This result is similar to that obtained by Lubbock (1888) 

 on daphnias, which were found to collect more freely in 

 yellow and green light than in daylight. 



Loeb appears to doubt the accuracy of these results. 

 Referring to those of Lubbock he says (1905, p. 10): 

 " One half of a dish was covered by a yellow screen; the 

 other half was left uncovered. In the uncovered half, 1,904 

 animals collected, while 3,096 gathered under the yellow 

 screen. From this Lubbock concludes that Daphnia has 

 a * preference ' for ' yellow.' But one would suppose that 



