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formsa kind of oxygenized pommade. The fat of the gryllo-talp treated with muriatic acid coagulates very quickly, but becomes less yellow, the muriatic acid giving it less oxygen.

From all that has been said, it is evident that it is exceedingly difficult, not to say impossible, by direct observations to know the ramifications of the dorsal vessel; but it would have been improper to have admitted proofs purely negative, without having attempted direct observations in the first place. The first means that presented itself was injections. To them, therefore, I had recourse in the first place.

The membranes of the dorsal vessel being very thin, oppose a great obstacle to the success of mercurial injections. Accordingly, the dorsa! vessel almost always bursts before the injection has reached its extremity; so that we cannot depend upon the results of such injections. Yet I ought to observe that, in those parts of the dorsal vessel in which the injection has succeeded, I have never observed the mercury make its way into a single fibrilla, or indicate the smallest ramification. This method appearing to me insufficient, I soon abandoned it, and tried various injections with liquids coloured with cochineal or indigo, according to the colour of the dorsal vessel. These injections, forced in by a very fine syringe, succeeded perfectly, especially in the larvae of the great butterfly (paon), and of the sphinx of the lithymale, and likewise in the mole cricket. In all of them, the injection having penetrated to the extremity of the dorsal vessel, this vessel always appeared to me a simple cylindrical canal without any ramification. I repeated these injections in a great number of individuals of each class, and I always had the same result.

Though these coloured liquids did not show any ramifications of the dorsal vessel, it was possible that these ramifications might become sensible by making this vessel absorb these liquids. For this purpose I put living insects into liquids strongly coloured, and allowed the absorption to take place through the pores of the organs. I had the greater hopes of success, because the conformation of the tracheæ gave me hopes that these vessels would absorb very little o the coloured liquids. In all the insects exposed to this kind of proof, I saw the pulsations of the dorsal vessel cease by little and little, and the humor contained in it coagulate. It was only after this coagulation that the membranes of the dorsal vessel absorbed the coloured liquids, and even much more rapidly than the other organs. This vessel thus coloured formed along the back a bluish or reddish line, which had no ramification whatever; but the white fibrillæ of the trachea were always distinguishable, which, as has been said, form the first membrane. In this absorption the trachea do not sensibly change their colour. They merely assume a deeper tint; but they sink down completely. The adipose tissue which surrounds the dorsal vessel assumes the form of clots. The muscles separate in such a manner that their fibres become perfectly distinct, and that their attachments may be easily recognized. The

liquid being at last evaporated, the indigo or carmine appears 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 trachea absorb the colouring matter; but the absorption was so' indistinct, that I merely mention it to put those on their guard who may wish to repeat these experiments. In the locusta I perceived often that the absorption by the membranes of the adipose tissue belonging to the muscular fibres, called wings by Lyonnet, was almost 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 inembranes 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 nor 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 perceived 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 I could have no doubt of the success of my injection. As I did not perceive ramifications, I 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 any coloured liquid would issue out; because by the preceding dissection I had of necessity cut the openings of the ramifications if they existed. Whatever care I applied to these experiments, varying 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 membranes of the dorsal vessel (the insects being alive), I saw the fat and the humour of the vessel coagulate, and then absorb the

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alcohol; but it was never possible to perceive the least lateral ramification. So constant an agreement in researches so delicate seemed sufficient to lead to the conclusion that the dorsal vessel of insects has no ramifications; but as I had not attempted every thing which it seemed possible to do to ascertain the point, I continued my researches.

The acids appearing to me proper to coagulate the humour of the dorsal vessel, I put some drops of nitric acid on this vessel. The contraction of the organ immediately ceased, but the life did not appear injured, and the insect continued to agitate its members as before. The dorsal vessel, and the humour which it contained, became whitish; and as the alteration gradually extended itself to the muscles, they also became whitish, but with a pearl-coloured lustre quite peculiar. The dorsal vessel filled with a coagulated liquor has thus become more easily observable. On lifting it up with precaution, I did not perceive the smallest fibrilla issuing from it, excepting the trachea which pass into it. It is always easy to distinguish these organs, because the nitric acid does nothing else than increase their lustre. I afterwards tried the action of various other acids, and always obtained the same results; only they appear more speedily when sulphuric acid of 69° is used. The action of acids is advantageous to enable us to follow the direction of the muscles, as they communicate to these organs a 'brilliant pearl colour, and render visible the bundles of which they are composed.

Injections made with solutions of tannin have always shown me the dorsal vessel without any kind of ramification. The same was the case when the solution was absorbed by the membranes of the vessel.

(To be continued.)

ARTICLE VI.

Observations on the Orthoceratites of Scotland.
By John Fleming, D.D. F. R.S. E.

(Communicated to the Wernerian Natural History Society, May 21, 1814.)

THE examination of the history of petrified bodies would be greatly facilitated by the adoption of some regular plan, calculated to give arrangement to the information already obtained, and to fix the attention on those objects which ought to be regarded as of the greatest importance. Thus our knowledge of this branch of science would very rapidly increase, were we to examine with care the characters of the different species, investigate the changes which they have undergone in the mineral regions, and ascertain the various rocks in

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