198 On the Uses of the Dorsal Fessel. [March, 



liquid being at last evaporated, the indigo or carmine appear^ 

 disseminated between the adipose membranes ; but not in an 

 uniform manner, as would be the case if these colouring matters 

 were contained in real vessels. 



In other attempts which I made I saw the membranes of the 

 tracheae absorb tiie colouring matter ; but the absorption was so 

 indistinct, tliat I merely mention it to put those on their guard who 

 may wish to repeat these experiments. In the locusia I perceived 

 often that the absorption by the membranes of the adipose tissue 

 belonging to the muscular fibres, called wings by Lyonnet, was 

 slmost as great as that by the dorsal vessel. It is evident that in 

 this last circumstance the coloured line formed by that-vessel ought 

 to be less perceptible. On examining these membranes with a 

 strong glass, we always see distinctly the colour forming a continued 

 line in the dorsal vessel, a continuity which we never see at the side 

 iior in the membranes. 



These first attempts being insufficient to detect the ramifications 

 of the dorsal vessel, I injected into it, and made it absorb liquids 

 capable of acting chemically on the humour which it contained. 

 Tincture of nutgalls strongly coloured with indigo and carmine, and 

 filtered, in order to have as few undissolved particles of colouring 

 matter as possible, was the first re-agent which I employed. This 

 liquid, forced into the dorsal vessel by an injecting syringe with a 

 capillary opening, made its way to the extremity of the vessel. I 

 repeated this injection at different times on the larvae of the 

 geotrupa nasicornis and great butterfly {paon), and likewise on the 

 mole crickets (while alive) ; but never peiceived the coloured liquid 

 to make its way into the smallest branch of the dorsal vessel. 



I then repeated these injections in a manner somewhat different ; 

 and to be certain that they would penetrate into the dorsal vessel, I 

 introduced a globule of fat into this vessel ; and in proportion as I 

 pushed the injection, the globule advanced in the interior of that 

 organ. Thus by little and little it came to its extremity, and then 

 1 could have no doubt of the success of my injection. As I did 

 not perceive ramifications, 1 dissected with great care the membrane 

 which surrounds the dorsal vessel, endeavouring to separate it as 

 completely as possible. Passing then a little filtering paper on the 

 side of the vessel, I compressed it gently, in order to see whether 

 anv coloured liquid would issue out; because by the preceding 

 dissection I had of necessity cut the openings of the ramifications 

 if they existed. \\ hatevcr care I applied to these experiments, 

 varving them, and repeating them frequently, I never perceived 

 any liquid issuing out. Sometimes, when my assistant did not 

 close completely the inferior opening of the dorsal vessel, some 

 portions of coloured liquor made its escape ; but it was always at 

 that extremity. 



Finally, having made the tincture of nutgalls to be absorbed by 

 the membrane^ of the dorsal vessel (the insects being alive), I saw 

 the fat and the humour of the vessel coagulatCj and then absorb the 



