PHENOMENA OF ORIENTATION EXHIBITED BY EPHEMERID/E. 387 



The second figure shows lights arranged along the lower edge 

 of a perpendicular surface at intervals of twelve to fifteen inches. 

 About each light was the usual excitement zone and upward from 

 this extended the radiating lines of insects in the optimum zone. 

 As shown in the diagram these lines were rarely at an angle of 

 less than 35 degrees. This was due to the fact that below this 

 point the lines from neighboring lights conflicted and caused such 

 confusion among the insects as to obliterate regular alignment. 

 The greatest confusion occurred in the comparatively short space 



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FIG. 2. 



between the lights where insects attempting to arrange them- 

 selves about one light constantly came into conflict with others 

 attracted to the neighboring light. 



When the insects rested on a horizontal plane about a light 

 they faced it. The most striking feature connected with the 

 arrangement of the insects on a perpendicular surface was that 

 the individuals on opposite sides of a horizontal plane passing 

 through the center of a light had opposite ends of the body directed 

 toward the light. The insects below the plane or parallel with 

 it faced the light, whereas those that were above the plane were 

 turned away from the light. In other words all the insects? 

 except those parallel with the horizontal plane, approximated a 

 vertical position with the anterior end uppermost. Those above 

 the plane and with the posterior end directed toward the light 

 were apparently as well content as those below the plane and 

 facing the light. 



The position of the insects on a horizontal surface shows that 

 other things being equal they face the light. It is reasonable 

 to conclude that their normal reaction to light is positive. The 

 negative position assumed on a perpendicular surface above a 

 light can be explained, in view of the air current and the inversion 

 experiments, as being due to the difficulty experienced in main- 

 taining a foothold in the inverted position. 



