REACTIONS OF ARTHROPODS TO LIGHTS 475 



tral lights of equal intensity, measured, not by the human eye, 

 but by accurate physical means. In this work are used five 

 species of insects belonging to three different orders as follows: 

 the larva and the adult of Calliphora erythrocephala Meigen and 

 the adult Drosophila ampelophila Loew of the Diptera, the 

 Zeuzera pyrina Linne larvae and the adult of Feltia subgothica 

 Haworth of the Lepidoptera, and the adult Periplaneta americana 

 Linne of the Orthoptera. 



3. :methods 



The apparatus used in these investigations is the same as 

 that described by Laurens ('11, p. 258) in his paper on the reac- 

 tions of toads to monochromatic light. An account of the con- 

 struction of the generators is given in greater detail in a paper 

 pubHshed by Day CU, pp. 310-315). This paper also includes 

 a short description of the radiomicrometer used in measuring 

 and equalizing the intensities of the colored lights. 



The essential features of the light apparatus are two light 

 generators placed at opposite ends of a dark chamber 80 cm. deep, 

 130 cm. long and 70 cm. high. In addition to the dark chamber 

 suitable screens and reflectors were employed to exclude, from 

 the animals during the experiments, any light not proceeding 

 directly from the prism. In order to reduce the amount of 

 diffuse light from the outside to a ixdnimum the entire apparatus 

 was constructed in a large dark room arranged for the purpose. 

 The special accessory apparatus for exposing the animals to the 

 light, which was adapted according to the nature of each organ- 

 ism to be tested, will be briefly described in the account of the 

 experiments given for each species. 



The colored lights used in this work were four in number as 

 follows: blue, 420 to 480 ntj.; green, 490 to 550 nij.; orange-yellow, 

 570 to 620 /i^; and red, 630 to 655 ixy.. These colors were 

 obtained by cutting down the spectrum by means of diaphragms of 

 blackened cardboard with narrow vertical slits of appropriate size. 

 The sources of the lights were Nernst glowers on a 220-volt 

 circuit. In order to equahze the intensity of the four colored 

 lights it was found desirable to used one glower for the red, two 



