32 INSECTA. 



iiciently well the functions of the large anterior veins, 

 and gives rigidity to the forward part of the wing, while 

 the flexible cloth membrane is essentially similar to a 

 membranous wing, if made stiff enough to maintain a 

 horizontal position when not in motion. If, now, this 

 artificial wing is carried slowly downward through the 

 air, it descends vertically, and the membrane remains 

 horizontal ; but increase the speed, and the wing, acted 

 upon by the resisting air, is driven downward and 

 forward, its vertical descent being changed to an in- 

 clined plane. When the wing is raised, on the other 

 hand, it is carried by the resistance of the air upward 

 and forward. Thus, by moving the rod vertically 

 with rapidity, the motions of insects' wings may be 

 imitated, and it will be found, even though the elbow 

 be held stiffly against the side and the hand simply 

 moved up and down, lateral motion being resisted, 

 that the hand and forearm are propelled forward with 

 a speed proportionate to the rapidity of the vertical 

 vibrations. In this way the action of the pliable 

 membrane of the wings in lifting and moving a body 

 through the air may be roughly demonstrated.^ At 

 times the wings are motionless, when the insect seems 

 to float through the air. This is owing, in part, to the 

 sustaining power of the wing surfaces, and also to the 

 fact that the weight of the body is lessened by 

 the prevalence and large size of air-vessels in the in- 

 terior. These, when inflated, increase the lightness of 



1 When the plane of the wing is changed, very different 

 effects are produced, as shown by an ingenious flying-machine 

 invented by Marey. (^Animal Mechanism. International Sci- 

 entific Series, Appleton & Co., New York, 1879.) 



