THE REACTIONS OF DROSOPHILA 77 



5. Effect of air currents. — The next question considered was, 

 How does Drosophila respond to air currents? Horizontal, up- 

 ward, and downward currents, produced by an electric fan, were 

 directed into a glass cylinder like the one used in the dark box. 

 Their strengths were so adjusted that the flies did not lose 

 their equilibrium. 



(a) Horizontal currents. — These trials, carried out in diffuse 

 daylight, did not give as definite a response as could be desired. 

 The flies were liberated singly from the bottle containers at the 

 open end of the cylinder, and their course of locomotion noted. 

 In only 11 trials out of the 40 made, could the response be called 

 definite. In 7 of these the flies crept against the current, in 2 

 they crept against it for about 10 cm. and then flew with it, and 

 in the other 2 they flew with the current. Every case of creeping 

 was against the current and every case of flying was with the 

 current. In the control experiments with no air currents the 

 flies crept or flew in any direction. 



(b) Upward vertical current. — In these trials 29.5 per cent of 

 the flies crept upward with the current, 59 per cent flew upward, 

 and 11.5 per cent crept downward. Gravity is here acting con- 

 trary to the force of the current and the 29.5 per cent creeping 

 up is probably a purely negative geotropic response. The creep- 

 ing downward was very slow and intermittent. The largest 

 number (59 per cent) flew with the current. 



(c) Downward vertical current. — The results of 61 trials showed 

 that 27.8 per cent of the flies crept upward against the current, 

 23.2 per cent flew upward, while 49 per cent flew downward with 

 the current. An interesting observation was that practically 

 all the flies crept upward a short distance before carrying out 

 the main response. In the control experiments, with no air 

 current and the cylinder in a vertical position, the only reaction 

 that could be noted was a negative geotropic one, the other 

 movements being indifferent. 



There is therefore a tendency for Drosophila to fly with the 

 air current, a positive response, and to creep against the current, 

 a negative response. Since there were extremely few flying 

 responses in the experiments with gravity and centrifugal force, 

 no comparisons can be made with them. But the creeping 

 against the currents corresponds with the negative response to 

 gravity and centrif ligation. 



