578 On the Usss of the Dorsal FesscL [May, 



organization which animals present. We may very well suppose 

 that the insects which decompose water in order to take possession 

 of its oxygen, have only a demi-respiration, while those that receive 

 air immcdiatelyj have a complete respiration. Those which receive 

 air innmediately, and have very considerable vesicular tracheae, with 

 an apparatus intended to keep them always full of air, ought to 

 have a respiration still more complete. And to adopt the ratio 

 which we have already pointed out, though fur from exact, the 

 respiration may be very v.ell doubled l)y ihai complication of means. 

 At least it is certain that the cartilaginous hoo])s which we have 

 compared to the ribs of animals with vertebrae, do not exist along 

 with vesiculary tracheae, except in tliose si)ecies which have occasion 

 for a great muscular power, from the great distances which they 

 are destined to travel. Such, for example, arc the locusts (crigiiets), 

 as famous for their emigrations, as for the ravages which they com- 

 mit in those countries where they stop in order to feed. Finally, 

 the ordinary vesiculary tracheae, or those which, not being very 

 large, do not require a particular apparatus for moving them, are 

 found only in species which require great muscular exertion, or 

 which, flying a great deal, ought to be able to diminish their spe- 

 cific gravity. Tlie caleopteres lamellicornes, and the lepidoptercs 

 and dipteres, are the insects in which this arrangement is most evi- 

 dent. Before passing to the particular description of the respiratory 

 organs of insects, we ought to explain what we mean by arterial 

 tracheae and pulmonary tracheae, insects exhibit in general two 

 orders of trachete, the uses of which not being the same (though 

 their organization is not very different) deserve to be distinguished.* 

 The one goes directly to the stigmata, takes air immediately, and 

 distributes it to the different parts of the body. The other does 

 not receive air immediately. It only communicates with the ex- 

 ternal air by means of the first order, and generally, being larger 

 than the arterial tracheae, serves as a reservoir of air. Then- direc- 

 tion, in general, is more regular, and their ramifications much less 

 numerous. These two orders of tracheae having then a different 

 object to fulfil, I thought that in order to render the description of 

 these vessels the clearer, it would be advantageous to distinguish 

 them. I have called the one arterial tracheae, because they are 

 branched like these vessels, and carry air to all parts of the body, 

 as the arteries distribute blood in those animals that have a real cir- 

 culation. But to perceive how far this analogy is well founded, 

 we must recollect, that in insects air is the only i^uid that is really 

 circulated. As to the pulmonary tracheae, as they serve as reser- 

 voirs of air to enable it to act onlhe diticrent parts of the body, 

 this name was the most suitable that offered itself. The two orders 

 of tracheae in iosects were recognized by Swammerdam, and, in 



* The greater number of anatomists h,id observed long a;;o, iliaf tliere exist 

 two orders of tracheae in insects, the one destined to introduce air into the body, 

 the olbcr to rarry it to all parts of the body. Itcaiimur thought Ihnt tlie insect* 

 drew in air by their stigmata, but that they threw it out from all parii of the 

 bodv. Mem. torn. i. p. 390, 409. 



