VANESSA IANTIOPA LINN. 459 



warmer (22° C.) than out of doors (13° C). I therefore opened the window and 

 door of the photographic room till it was approximately as cool as outside, and after 

 having exposed the butterflies for over an hour to this temperature, I repeated my 

 former experiments. But the insects were as strongly positive as at first. 



The negative orientation observed in the field took place in full sunlight; the 

 experiments in the laboratory were made with diffuse daylight. Hence it occurred 

 to me that light intensity might have something to do with the sense of the photo- 

 tropism. I therefore repeated my experiments in a cool room, into which sunlight 

 entered by several windows. But here also the butterflies flew even through the 

 sunlight to the windows. The sunlight entered the room at angles of approximately 

 45° with the vertical windows and with the floor, and it was interesting to observe 

 that as the butterfly entered the direct sunlight from a window, it did not change 

 its course in reference to the sun's rays, but cut their path even at right angles, flying 

 straight on toward the window. In this respect my observations are quite different 

 from those of Loeb ('90, p. 51) on Papilio machaon, which is said to fly in the direction 

 of the rays of light. 



To test the influence of light intensity more accurately, I liberated several butter- 

 flies, one at a time, in a room lighted only by an incandescent lamp of about two 

 candle-power. The insects, which were liberated at a distance of two metres from 

 the light, flew toward it in all instances and circled irregularly about it. A similar 

 reaction was observed toward light from a small arc lamp of about 250 candle-power. 

 When an ordinary gas-flame was used as the source of light the butterflies flew into 

 it and singed their wings much as moths would do. Not infrequently the butterflies, 

 on their way to a window or a distant light, would settle on the floor or on a table 

 and would creep before beginning flight again. In all such instances they crept 

 toward the source of light, that is, they showed positive phototropism, and never 

 even when resting in the sunshine in the room did they show the least evidence of 

 negative phototropism. Thus whether creeping, flying, or resting, in weak or in 

 strong light, in a warm or a cool room, the butterflies tested in the laboratory were 

 always positively phototropic. 



To discover the reason for the apparent contradiction between my observa- 

 tions made in the field and those made in the laboratory, I caught in a neighboring 

 wood on a sunny day two specimens that I observed to settle in the characteristic 

 manner with the head away from the source of light, and transported them at once 

 to the laboratory for experimental observations. When liberated in the photo- 

 graphic room, they flew toward the window; they likewise flew and crept toward 

 artificial fight. When placed in a large black box with electric fights one at either 



