1815.] On the Uses of the Dorsal T'esscl, 377 



that decompose water in order to obtain its oxygen. It is obvious 

 that those insects which breatlie air immediately, ought to be the 

 only ones in which we find the two kinds of trachccfi of which we 

 have spoken. The vesicular tracheae would not have sufficient elas- 

 ticity to drive out the superabundant water, wliich the insect intro- 

 duces into its tracheide. Perhaps this elasticity would not even be 

 sufficient for those which live habitually in water, but do not de- 

 compose that liquid. In the second place, tlie insects which de- 

 compose water ought to be the only ones that have but one stigma. 

 This stigma ought to be so placed that the animal may receive the 

 water necessary for it ; and we see that whenever this disposition 

 exists, it is always at the anus that tills opening is found. But 

 before passing to the description of all these dillorent kinds of 

 organization, we shall here give a table wliich will render thera 

 obvious at one view. 



1. Respiration in Air. 



I. With tubular J Division I. — Arterial trachcse. 



tracheae \_ Division II. — Pulmonary and arterial tracheje. 



r\. With • cartilaginous 



■ 



II. With vesicular J Always two orders^ hoops, or a kind of ribs. 



, Without car 

 hoops or ribs. 



tracheiE \ of trache<e .... j 2. Without cartilaginous 



II. Respiration in Water. 



rBreatliing by true stigmata, and 

 rDivisIon I.< coming to the suiface of the 

 Only with tubu-J i. water to breathe air. 



lur tracheae . . . j rBreatliing by an opening placed 



[_DivIsion II. "I at the anus, decomposing 

 l^ water. 

 This table shows us that the result of respiration, or the oxyge- 

 nation of the blood, or of the humour which comes in place of it 

 in insects,* ought not to be the same in the different modes of 



* By tlie c.x^reis\an oxygenation of the blood, T do not pretend to affirm that in 

 respiration a poiiioii of oxygen is tixed in the l>loud, and that there is altvayt » 

 diniinutiun in (he ^ol(lnle of uxvgen. Thou<;h this opinion has been supported bj 

 the motit gitilful cheiuibis, aj Lavoisier, (loodKiu, Davy, and Benliolli't, H'e must 

 acknowledge that tlie expcrimenls of Crawford, and cspceially those of Allan 

 and IVpys, seem to oppose that opinion. Thomson, to wlioiii we liketvi^(r owe 

 cxperiinents on the same snbjeet, Iku observed, that the diminution of vnhinic of 

 the oxygen is rrot constant; and he eonsiders it as an elfcct unionnerted with 

 respiration. But whe(hiT respiration produces nulj a detarbonization of the 

 blood, that it to sav, that the volnine of oxygen abMiilirJ represents exartly the 

 volume of carbonic arid gas expired ; or wliether there be a diminiilion in the 

 oxygen, be^ide> that which has served to the production of carbonic acid at the 

 expense of the blood, ue tliought lli:it we niij(hl employ the word oxygenation 

 •f (lie blood, bacanse it ig more convcnicut ill explaining the physiological pbc- 

 liomena of respiration. 



We thall put the reader in mind here, that .M. Vau(|uelin proved long ago the 

 ncceisity of oxygen in the ritpiration of insects, and that common air rctnini 

 «earcely any oxygen when these aniiiidls can no longer live in it. Tlie air which 

 we expire, on lli>- contrary, is coinpuM-d of three carhouic acid, IH OAVgen, aud 

 79 azote. See Ann. de Chiin. toiu. .xii. p. 'iTJ aud JS'.'. 



