38 STUDIES IN GENERAL PHYSIOLOGY 



strange object" drives the moths into the flame. We find, 

 however, that the caterpillars of Porthesia chrysorrhoea 

 creep as well toward the sun as toward a lamp. Yet, 

 according to Romanes, the sun ought to be a familiar ob- 

 ject to these animals. Such anthropomorphic opinions as 

 those of Romanes are evidently as useless in the analysis 

 of life-phenomena as the speculations of metaphysicians 

 e. #., Hegel's on physical phenomena. A scientific analysis 

 of the behavior of moths toward light leads to a very simple 

 explanation of the paradox. 



Experiment 1. Specimens of Sphinx euphorbiae, Bom- 

 byx lanestris, and other moths are kept in a large glass box. 

 The box is placed in a room into which only daylight and no 

 artificial light enters. As soon as the animals begin to 

 fly, at the approach of twilight or later, they collect at the 

 window side of their boxes. Whenever the box is reversed 

 the animals fly back to the window side. This experiment 

 is rendered more complete by the following observations: 



I kept the pupae of moths in an open box. Most of 

 the moths hatched at night. On the following morning I 

 always found them collected at the closed window of the 

 room. Here they remained all day exposed to the light. 

 Finally, when I caused the moths to fly by day, I noticed 

 that they flew to the window as do all other positively 

 heliotropic insects. These experiments show that the 

 animals are attracted, not only by a lamp, but also by 

 diffuse daylight. They also show that Reaumur's idea that 

 moths shun daylight is wrong. The experiments indicate 

 that the animals are positively heliotropic toward diffuse 

 daylight, although, as we shall soon see, this positive helio- 

 tropism may during the daytime be obscured by another 

 form of irritability. 



Experiment 2. I brought some specimens of Sphinx 

 euphorbias into a room which had a window only on one 



