PHENOMENA OF ORIENTATION EXHIBITED BY EPHEMERID/E. 385 



insects were upside down. The overhanging abdomen disturbed 

 the equilibrium of some of them sufficiently to cause them to 

 lose their hold and fly off. The others retained their footing, in 

 some cases by changing the position of the legs, and remained in 

 the inverted position for ten to fifteen minutes which was as 

 long as they were watched. 



In explanation of the position normally assumed on an upright 

 surface the evidence derived from the experiments seems to 

 indicate that the position taken is not a negative reaction to 

 gravity per se but that it is largely, if not entirely, due to the 

 character of the insect's means of attachment. 



Results obtained from experiments performed to test the in- 

 fluence of a breeze upon the position of the insects on a perpen- 

 dicular surface support this view. A current of air was directed 

 against the side of individuals resting in the normal upright 

 position on a perpendicular surface. As they turned the current 

 was so directed as to bring them still further around. During 

 the process some of them could not retain their foothold and 

 flew off. The others turned completely around and faced directly 

 downward. They maintained the inverted position at least as 

 long as they were under observation, ten to fifteen minutes, 

 which length of time, in view of a constant coming and going 

 among those normally situated, seemed sufficient. 



REACTION TO LIGHT. 



The conclusions with regard to reactions of the Ephemeridse 

 to light are largely the result of observations made in the amuse- 

 ment resort already mentioned. The observations have to do 

 mostly with artificial light. The insects react negatively to bright 

 sunlight and seek the shade. They are strongly attracted to the 

 lighter colors of artificial light. In the resort there are a great 

 many electric lights of sixteen candle power intensity with colorless 

 glass bulbs. Many of them are attached in a horizontal position 

 to the sides of buildings in such a way that there is a perpendicular 

 surface either above or below them and frequently on all sides. 



The reaction to these lights seems to be satisfied if the insects 

 can come to rest within a zone which begins approximately six 

 inches from the light and covers a radius extending outward for 



