HELIOTROPISM OF ANIMALS 11 



tions of the dish. When half of the vessel was covered 

 with an opaque porcelain screen, Lubbock found 2,04S 

 animals collected under it, and 2,932 animals in the un- 

 covered half. From these and similar experiments Lubbock 

 concludes that the animals have a decided preference for 

 yellow light. 



I also have made some experiments on the effects of 

 rays of different refrangibility on Daphnia, and found that 

 when the more refrangible rays (blue and violet) fell 

 upon the animals they hastened to the source of light and 

 moved up and down on the light side of the vessel. When 

 I made the same experiment with the less refrangible rays, 

 the effect was weak or did not take place at all. The result 

 conforms with other facts which are to be described later. 

 I shall, therefore, not revert to the Daphnia and their 

 alleged "preference for yellow." 



Lubbock has employed a similar method in his experi- 

 ments 011 wingless ants; 1 these, however, led to much more 

 fruitful results than his experiments on Daphnia. In an 

 experiment in which a vessel was covered with strips of 

 red, green, yellow, and violet glass he found that 890 

 animals collected under the red glass, 544 under the green, 

 41)5 under the yellow, and only 5 under the violet. There 

 is no doubt in this case that the animals collected under 

 those glasses where they were struck by the less refrangible 

 rays. Other experiments showed that red glass acts like an 

 opaque body. 



The observation of Lubbock that ants avoid the ultra- 

 violet part of the spectrum is also worthy of note. For the 

 sake of completeness the experiments of Lubbock on bees 

 and wasps must be mentioned, in which it was found that 

 under otherwise similar conditions blue objects smeared with 

 honey were preferred to those of another color. 



'LUBBOCK, "Amrisi-u, Hii-ncn mul UV-prii," iliiil., 1883. 



