NOTES AND MEMORANDA.

A New Organ (?) of the Rotatoria.-Dr. Pelletan writes in the 'Journal de Micrographie,' that having for several years undertaken a series of researches on the Rotatoria, and particularly on the Rotifers, he has come to the conclusion, that these beings are very insufficiently known, and that many observations, particularly abroad, seem to have been embellished by their authors so as to resemble somewhat a romance.

"In January last I found in some Zygnema, which I had preserved in an aquarium for nearly a year, a great number of rotifers without eyes, furnished with two rotatory lobes of small dimensions, with mastaces of numerous small teeth, and which seemed to me to be the Callidina elegans of Ehrenberg. A singular detail struck me. One of them had on the flank of the long segment that may be called the abdomen, a small hyaline vesicle with a double outline, which did not disappear whatever movement the animal made. I considered it at first a parasite, and I pressed a little on the covering glass in the neighbourhood of the rotifer in order to try and detach it. Not far from it two other animals of the same species, which not long previously presented nothing abnormal, had now each a vesicle, but one had it on the right and the other on the left of the abdomen. With a objective I established in the clearest manner that these rotifers carried on each side of the body one and perhaps two stigmata. These stigmata opened and shut as if by a sphincter; they were placed on the summit of a little papilla, situated towards the lower third of the length of the abdomen. When shut they appeared like a point surrounded by a circle, indicating a subjacent vacuole, and bordered by small radiating wrinkles, formed by the integument contracted by the sphincter. When open they presented a festooned border with a clear bottom. I saw them open and shut alternately under my eyes, like the contractile vesicle of a Paramecium, but without regular rhythm; the contraction appeared to me to be voluntary. Seen in profile they constituted a perforation of the integument, and the hernia of the subjacent vesicle by their meatus consequent on the compression, clearly proved to me that the meatus opened to the exterior. As many times as I wished I was able to establish this phenomenon and to cause the hernia. This when produced did not return any more, at least for several hours, and when the animal contracted itself into a ball the hernia persisted.

It is possible that the fact has already been established, but I am not aware of it. I have inferred from it that the mode of respiration amongst the different species of rotifers has been insufficiently known to me, for these stigmata or stomata belong evidently to the respiratory apparatus, and seem to me to have no other end than to admit the aerated water through the thin walls to act upon what may be called the hematose, without the intervention of aquiferous canals, since the vesicle constitutes a close cavity.

It was important to verify the number and exact situation of these

stigmata, but unfortunately the incessant movements of the animals rendered the observation difficult, and I have been able to provoke on each of them only the hernia of a single vesicle.

The aquarium having subsequently frozen, the plants and organisms were destroyed. Since then I have never been able to find the rotifer in question. Perhaps I have had to do with the larval state of a species better known at an adult age. I have not the least doubt that my observation was exact-it conformed to what is known of the respiration of certain classes of worms."

A Method of Preserving the Rotatoria, Infusoria, &c., with their Organs Extended.-Referring to the preceding observations, Dr. Pelletan writes :-"The result showed me the necessity of resuming them hereafter, but upon animals rendered immovable at the moment of complete activity, and in all the positions that they are capable of taking. In fact, their extreme mobility and continual changes of form, due to their contractility, are a serious obstacle to their study, and it is only by a long course of fatiguing observations that the same animal can be seen in its different states of extension and under its different aspects so as to obtain a fairly complete idea of it. I therefore endeavoured to find a method which would enable them to be fixed in all attitudes, to preserve them in that state so as to study them in the same way as histological preparations and with high powers, which is ordinarily very difficult with living animals. Under the influence of all the reagents, even with narcotic or anæsthetic agents, the rotifers immediately contract and become only a small globule, in which all the organs, crowded one on the other, show nothing distinctly. It was necessary therefore to find a fixing agent which would enable an absolutely instantaneous effect to be produced. This reagent is osmic acid. It has always furnished me with excellent results, and I am not aware that it has been previously applied to the preparation of the Rotatoria and Infusoria.

Everybody knows the property which osmic acid has of fixing the histological elements instantaneously in their actual form, but it is not sufficiently known that to act with this instantaneousness it is not enough that it should be concentrated, but it must be employed in a way that its action should not be too much dissipated. Thus if a drop of a solution of 1 per cent. is placed on a tissue, the exact point where the drop has been placed is almost immediately fixed, but the neighbouring parts, over which the acid is diffused and acts only, so to say, at second hand, are subjected to a very much feebler action. If a more concentrated solution is employed there is not much difference in the effect-the action of the acid is exhausted upon the point immediately affected, and does not extend to any distance. It is thus that M. Ranvier has shown that the arms of the hydra may be fixed instantaneously whilst extended, notwithstanding the exceeding rapidity with which they retract them, but the drop of acid must be placed directly upon the little polyp, which can be best done by the ordinary dipping tube.

It is in an analogous manner that I operate on the rotifers and the contractile infusoria. I put about half a cubic centimetre of the

solution on the preparation, and at the very moment of the cataclysm all the living beings, animal and vegetable, are instantaneously rendered immovable. I then expose the preparation to a current of air, which takes off the disagreeable vapours of the acid and evaporates the greater part of the water.

I have treated in this manner some filaments of Vaucheria collected in March last, and I found that they preserved their form and colour— the protoplasm was not retracted, and they were in fructification. The antheridia and the oogonia were visible with a tint of green much deeper than the rest of the filaments, and containing globules of fatty matter, which the acid had coloured brown or black. The ribbons of the Diatomaceæ, Himantidium pectinale, the zigzags of Diatoma vulgare preserved their natural aspect and tint, the isolated Navicula floated in the preparation with some Cosmarium and Closterium of a green as bright as if they had never been subjected to the action of any reagent, but the motile corpuscles of these Desmidiæ were for ever arrested. Here and there were some Infusoria (Paramecia, Stylonichia), &c., of a light brown colour-immovable with all their cilia arrested; an Euglena viridis of a brilliant green showed its red ocular point and its long flagellum,-all these beings, in a word, seemed still living, and their protoplasm had not changed in form. In the diatoms some globules of a light brown indicated their oily nature, but no other modification appeared to have been produced.

The contractile animalcules were found in all positions. Certain Vorticelle were immobilized in a complete state of extension, and their peduncle had lost its elasticity. The cuticle ordinarily remained uncoloured, but the internal parts and the muscle of the peduncle were brown. The rotifers were in all attitudes; some completely developed, the wheels exposed and bordered with cilia, which could often be counted. I have counted twenty on the wheel of a Philodina erythrophthalma, of which the ocular points, oblique and elongated, like the eyes of a Chinese, remained red. It can easily be established thus that the rings of their bodies, articulated like a telescope, are much less variable than they are ordinarily said to be.

In short, all the living animals were immobilized in the position which they occupied at the moment that the acid touched them.

The preparations thus obtained can be preserved-by passing over them some glycerine the diatoms, desmids, rotifers, and infusoria do not contract, and the preparation can be sealed down. In the Confervæ and the other filamentous algæ, however, the protoplasm is subjected by the glycerine to a very notable shrinking. It is preferable, therefore, to preserve the preparations in a 1 per cent. solution of carbolic acid.

Finally, I should mention that the reagents ordinarily used in histology, and particularly the colouring matters, may be applied to the animalcules. I will give in another paper the very interesting results obtained by these methods, but I should say now that in consequence of the strong action of the osmic acid on the animals (giving them a brownish tint), they colour badly or confusedly by the generality of colouring matters. The method which I have hitherto found

preferable is impregnation by a solution of chloride of gold-1 in 400 or 500. The chloride acts in preference on the points where the osmium is already deposited. Its action is, as is known, very inconstant, and the tints which it gives very variable; but the different parts of the same animalcule, coloured a uniform yellowish brown by the osmium, are differentiated in various tints by the action of the chloride. In a Philodina I found the integuments colourless, or of a light blue, the muscular bands rose, the intestinal tube brown, the cloaca black (being full), the glandular masses violet, and showing clearly the vacuoles and the rounded cells, with nucleus and nucleolus. The operative process is very simple. It is only necessary to pass the solution of gold under the preparation very slowly, so as not to carry away in the current and lose the animals which are floating. I place a drop of the solution on the edge of the glass and produce on the opposite side a very gentle suction by means of a piece of blottingpaper, which has been passed through the vapour of boiling water, so that without being wet it is not dry, and so that its suction only operates in proportion as it dries. I then place the preparation in the light and wash it (in the same way) with a current of distilled water until the excess of the chloride solution is removed. If the tints are too pronounced the preparation can be treated with a drop of very diluted formic acid, or mounted in glycerine.

I have obtained less satisfactory results when the chloride is put upon the preparation after the osmic acid-the deposit is much more irregular in consequence of the presence of osmic acid in excess, which produces a confused precipitation of the gold."

A New Form of Hot Stage.-In the 'Bulletin de la Société Belge de Microscopie' (vol. iv. 103) an ingenious form of hot stage is described by M. Renard, the invention of MM. Vogelsang and

Geissler, and used by them in their investigations on liquids enclosed in the cavities of crystallized minerals. It is said to enable the temperature of a preparation under the microscope to be appreciated with great exactness, and at the same time the phases of the dilatation of

the liquid to be followed corresponding to each degree of temperature. The essential part of the apparatus consists of a thermometer (T), the "bulb" of which, instead of being spherical, is formed into a ring. The thermometer is attached to a brass plate which lies on the stage of the microscope, and the ring is so placed that the interspace coincides with the opening in the stage, and allows the light from the mirror to pass through it. On each side of the ring and soldered to it are three glass "knobs," to which is attached a platinum wire, which crosses above the ring from side to side, serving as a support to the preparation in conjunction with the two pieces S. This wire is attached at b, b, to two thicker wires of copper, which are kept in place by the screws at E, and when heated by a battery communicates the variations in temperature to the thermometer through the knobs. With a battery of two Bunsen elements the thermometer will register 200° (C.), although such a temperature is not practically necessary, as at 150° Canada balsam boils.

Immersion Paraboloids.-Dr. James Edmunds writes to 'Nature' of 11th July:-"The immersion paraboloid illuminator exhibited at the recent soirée of the Royal Society, as designed by me, proves to have been anticipated in principle and construction by Dr. John Barker, of Dublin, from whom a paper on the subject will be found in the Proceedings of the Royal Irish Academy for 1870. An immersion paraboloid illuminator was also described by Mr. Wenham in the Transactions of the Microscopical Society for 1856. My paper on the subject appeared in the Monthly Microscopical Journal' for August 1877, but that Journal being defunct, I ask you to allow me to credit these gentlemen with a priority which on perusing their papers I find to be due to them. I ought to add that until the construction by Messrs. Powell and Lealand of my illuminator, the device had never come into practical use, and that so far as I can learn, no reference to it exists in any optician's catalogue or text-book on the microscope."

Organisms suspended in the Atmosphere.-M. P. Miquel has presented through M. Pasteur a note to the French Academy on this subject. He says:-According to M. Charles Robin the atmosphere presents (besides all kinds of debris) spores, pollen, skins of insects, and (rarely) eggs of infusoria. According to Drs. Maddox and Cunningham, who have confirmed M. Robin's results, the number of the different cellules distributed through the air is independent of the velocity and direction of the wind and of moisture. The collecting apparatus which Drs. Maddox and Cunningham made use of consisted of an aeroscope acting under the influence of the wind, and at each experiment the glycerined plate with which it was furnished remained for twenty-four hours exposed to the action of the wind. Once only the number of the microbia collected reached the maximum figure of 380, after deducting all bacteroid particles.

The results which I have arrived at after eighteen months of daily investigation differ in many points from those which I have just referred to. For the present I shall only deal with the statistical side of the question.