PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 243 



But Cbabrier was soou carried away by au exaggeration similar to 

 tliat of Borelli and of Xavier, tliongli in a contrary direction. Accord- 

 ing to him, an insect needed au insignificant force for its propulsion iu 

 space. No eftbrt was necessary to sustain it in the atmosphere; the ani- 

 mal floated there like an inflated balloon. In order to fly, it filled its 

 multitude of respiratory canals with air, and this, becoming heated, raised 

 the animal as it elevates a hot-air balloon. It is not necessary to say 

 that this conception of au aerostatic insect is au error. Without doubt 

 au insect, before attemptiug a flight, lays in a quantity of air by a sud- 

 den respiration, but this provisiou of air contributes only an insignifi- 

 cant part toward the end which Chabrier assigned it. 



The greater portion serves to prepare the organs of flight for the opera- 

 tion of their function. Jurine, of Geneva, in particular has shown that 

 the nervures of the wing membranes are small tubes, which only acquire 

 the rigidity aud extension necessary to flight by inflation with air. We 

 must refer to another contemporary, Strauss Durckeim, to find the ele- 

 ments of the theory to which juy observations have conducted me. In 

 his book on the Theology of Nature, a vast chaos of iugenious ideas, iu 

 which some profound, among many puerile, thoughts are to be found, there 

 are many tacts essential to the solution of our problem. Strauss 

 Durckeim has conceived the ideal type of the insect-wing, the diagram- 

 matic wing; that is to say, has reduced the organ to its essential parts. 

 It consists of a rigid nervation or frame-work in front, a flexible web 

 behind; this is all the apparatus. An apparatus thus constituted pos- 

 sesses the essential requisites for flight; otherwise constituted it will not 

 serve this purpose, as is the case with the false- wing of the Phryganidcc, 

 which has its principal nervation behind. It is enough that such a 

 structure should be made to rise and fall successively ; the forward 

 border being ridged and the other flexible, it naturally disposes itself iu 

 an inclined position, receiving the reaction of the air obliquely, and 

 thus transforms a part of the vertical impulse into a horizontal force. 

 The two parts of the wing above mentioned are both indispensable in 

 the same degree their respective offices comjilement each other in pro- 

 ducing a single result. Ingenious experiments, due to M. Girard, throw 

 light upon these facts. Destroy the anterior nervation, without remov- 

 ing the thin membrane, and the insect cannot fly ; destroy the flexibility 

 of the membrane by covering it with gum, and flight also becomes im- 

 possible. Here we cannot urge the objection that the superincumbent 

 matter interferes by its weight like a burden which weighs down the 

 animal; for, following out the experiment, we see that as soon as the 

 coating becomes dry, small fissures are produced, flexibility reappears, 

 aud with it the possibility of flight returns. These observations assist 

 us in comprehending the part which the anterior portion of the wings 

 of the Phryganidw play; which constitute the analogue of the stiif 

 nervure, while the hinder wings represent the flexible membrane. The 

 two wings of au insect thus complement each other. 



I shall not further prolong this retrospect. I have limited it to the 

 essential ideas entertained by our predecessors, aud to those which will 

 serve us iu the future. The preceding experiments, joined to those 

 which you have seen performed under your own eyes, seem to me to 

 establish the following facts, namely: The motions executed by an 

 insect during flight are limited to an elevation and a depression of the 

 wings. It is true that other motions take place in the wings of insects. 

 They are seen to move backward, and in repose to extend parallel to 

 the axis of the body. We also see insects moviug their wings backward 

 aud forward iu preparatiou for flight. But these motions are not directly 



