WINGS AND FLIGHT. 141 



the stick towards the paper slip. When the down- 

 stroke (DS) is made, the resistance of the air throws 

 the paper relatively up, and the air is reflected 

 from its surface, as indicated by the arrows. Simi- 

 larly, when the upstroke (US) follows, the paper is, 

 by resistance, thrown into such a position that the 

 air is reflected in the same direction as before, so 

 that both ascending and descending strokes give 

 an identical current. Simple mechanics shows that 

 the current from right to left in the Figure, by re- 

 action, tends to move the paper and stick from left 

 to right. Applying this now to the bee, whose 

 pliant wing-membrane yields to pressure like the 

 paper, we learn that both up and down strokes pro- 

 duce a current towards the costal nervure, and from 

 the posterior edge ; or, in other words, that the bee's 

 wing itself is moved in space, the costal nervure 

 going first — i.e., the bee flies forward. It is un- 

 doubtedly interesting to thus note how both up and 

 down movements aid in progression in one line. Yet 

 this fact but opens up another inquiry, for, if the 

 bee were only able to fly forwards, her plight in its 

 measure would resemble that of a steamship which 

 could not reverse her engines ; they might be stopped, 

 but she would remain under weigh, to possibly com- 

 pass her own destruction ere her initial velocity had 

 become expended. But a little attention in an apiary 

 will make evident that bees are competent to wing 

 their course backwards. As young ones come out 

 for their first airing in the warm mid-day sunshine of 

 soring, they fly constantly looking to the hive door, 

 advancing and receding in curves, so that the head 



