22 STUDIES IN GENERAL PHYSIOLOGY 



the neighborhood of a box containing the animals, those 

 which reacted at all always flew with great violence to the 

 side of the vessel which was turned toward the light. In no 

 case did they fly in the opposite direction. The experiment 

 was unequivocal and could be interpreted in but one way. 

 So far as the contact-irritability is concerned, the animals 

 collected in the four concave vertical edges when kept in a 

 cubical wooden box, which was covered on top with window 

 glass. In this position they assumed an indifferent orienta- 

 tion toward the source of light. To make perfectly sure of 

 this fact, I employed the following method : I placed a 

 plate of window glass so close to and parallel with the plane 

 of the floor of the vessel containing the animals that they 

 could just wedge themselves in between the floor and the 

 window glass. The glass plate was entirely exposed to the 

 light. Those animals which by chance came to the edge of 

 the glass plate crept under it, and remained in this position 

 exposed to the light, in contact, however, both above and 

 below with solid bodies. On the next day all the animals 

 were under the glass plate. The animals are therefore forced 

 to bring their bodies in contact with other solid bodies, and 

 it is this (and not the light) which causes them to creep 

 under solid bodies. I placed a ball of paper in the vessel 

 containing the animals ; a part of them crept under the paper 

 and a part into its folds. In nature these butterflies remain 

 in the clefts on the bark of trees or on the ground in mead- 

 ows. 



Forficula auricularia are found in great numbers in verti- 

 cal crevices (such, e. g., as the spaces between gate and gate- 

 post, in the entrance to gardens). I obtained the animals 

 for my experiments by hanging a cloth of cotton on the top 

 of a small grape vine. The animals collected in the folds of 

 the cloth. These animals in reality move away from the 

 light ; that is to say, they are negatively heliotropic ; but it 



