PHENOMENA OF ORIENTATION EXHIBITED BY EPHEMERIDyE. 383 



as before; the insects faced the current. However, when a 

 current was directed from the rear longitudinally along the dorsal 

 surface of the body the previous results were not repeated. In 

 some cases the insects crawled with the current and away from 

 the point of origin. In other cases they remained stationary 

 and took an attitude similar to that assumed when facing the 

 current. If the current became very strong they either attempted 

 to crawl away or they retained the attitude until blown off their 

 feet. When the current veered sufficiently to strike them on the 

 side they began to turn toward it. 



In these experiments with air currents the first noticeable 

 response from the insects was an attempt to hold on to the surface 

 upon which they were resting. This they did by fastening their 

 claws firmly and even changing the position of the legs. When 

 the current became so strong as to make it difficult to remain 

 attached and especially when the body was blown over to one 

 side the insects began to change position, rather hesitatingly it 

 appeared, and to face about toward the direction from which the 

 current came. When an insect reached a position where it did 

 not seem to have difficulty in maintaining its hold it came to rest. 

 This usually meant that it was directly facing the current, al- 

 though sometimes it stopped at a point between a half and a com- 

 plete about face. A half about face could generally be made 

 complete by increasing the strength of the current. 



When directly facing a current of air an individual is in the 

 optimum position for resistance; it presents the least surface 

 and the claws because of their backward curve have the maximum 

 effect in holding the body. On the other hand when an individual 

 stands sidewise to the current a greater surface is presented, 

 the claws are not in a relatively favorable position and attach- 

 ment is clearly more difficult. W T ith regard to the more rapid 

 reactions which result when the current strikes the wings it 

 may be said that the proportionately great expanse of the wings 

 above the body's center of gravity gives them such a leverage 

 that the body is more easily tipped over, a strain is more quickly 

 felt and attachment more quickly made difficult. In those 

 cases in which a current struck wingless individuals from the 

 posterior there was practically no obstruction to the current 



