line of fault of 3,000 feet. This operation was followed by a long period of denudation, and this by a post-tertiary depression, which the author terms the "Sahara submergence," after which the land was re-elevated at least 3,000 feet, but perhaps considerably more. A gradual subsidence appears to be still taking place.

NOTES AND QUERIES.

HOW TO PREVENT MOULD.-Will any reader of SCIENCE-GOSSIP inform "F. J. S." how to prevent mould in fern-cases?

TO POLISH SHELLS.-Having noticed in your magazine for February the question asked "How to polish shells," page 39, I send the following receipt which I have seen used, and know answers well.When you have collected your shells, wash them in clean water, and then prepare two-thirds water and one-third muriatic acid. Having first placed your shells in a glass or basin, then pour the water upon the shells, afterwards the muriatic acid; let them remain in this a few minutes, then take them out and wash them again in clean water, rub each shell dry with a piece of flannel (fine, of course), finish them over with gum-water, using a camel-hair pencil for the purpose.-Elizabeth Edwards.

LADYBIRD.-The etymology of lady-bird," a name given to various species of Coccinella, although pre-eminently to C. septempunctata, can be easily traced. That it was dedicated to the Virgin Mary, Our Lady, is evident from a glance at the word Marien-käfer, the German name for the insect. The same beetles are popularly known as lady-cows, -flies, or -bugs. Some view the affix bird as a corruption of bug, but they seem to overlook the fact that our glow-worm was once known as the glow-bird, and surely that beetle was never known as the glow-bug. Mr. E. Adams, quoted by Wedgwood, starts a different conjecture: the name "was probably given as seeming more appropriate to a flying creature (than that of lady-cow); but bird may here be a corruption of bode or bud, a name given to insects of different kinds, as sharn-bode, dung-beetle, woolbode, hairy caterpillar." He further says, "The beetle, whose spotted back might scarlet-red surpass," was not termed a bug on account of its colour, but obviously from its disagreeable odour. But what could be more offensive to eye and ear than thus placing the Virgin Mary side by side with the horror of many a honest household. The name cow is not readily traced; we are forced to reason from analogy. If Ocypus oleus is called a coach-horse in England, and an oa in Iceland, and if Geotrupes stercorarius is known in Poland as a "little cow," why should not a lady-bird be a cow too? I suppose to an entomological ear the affix "fly" is positively excruciating, but here we must deal tenderly with our forefathers, and remember that when they named the creature biology was in its infancy, and every insect that possessed organs of flight and was not identical with the beetle or the butterfly, was as a variety of fly. The lady-bird is the Lady of Flanders," and has other aliases too numerous to mention."-E. Halse.

66

HOW TO CUT SLICES OF COAL.-Can any reader inform me how to cut thin sections of coal? In most works on the preparation of microscopic objects, the

authors say the coal is macerated for about a week in a solution of carbonate of potash, at the end of which it is possible to cut tolerably thin slices with a razor. I have numerous pieces in solutions as above, and I find after being in even for months they are as hard as when first put in. Is it requisite to have any special kind of coal?-if so, what kind? I shall be glad of any information upon the subject. -J. G., Croydon.

THE ORIGIN OF WINDOW GARDENING.-I shall be extremely obliged if any of your readers can inform me anything as to the origin and early history of this now popular, and I might add fashionable, branch of floriculture, together with the names of the earliest plants and flowers used for this purpose.-B.

THE MYSTERIOUS MOUSETRAP.-I see in last month's SCIENCE-GOSSIP that Joseph J. Warry wonders what removed the mousetrap and ate the mouse. Very likely it would be its brethren. A few weeks ago I bought a penny mousetrap and set it at night. In the morning I was surprised to find a mouse partly pulled through the wires, with its head eaten off. The trap had been removed a short distance from the place I set it, through the other mice trying to pull it through the wires, I suppose. Most probably Joseph J. Warry's mouse ate all the bait in the trap before it fell a victim to its brethren. -Jno. Staincliffe.

MARINE AQUARIUM.-I think "J. G." can obtain sea-water from any dealer in aquarium requisites for about sixpence a gallon. Mr. King, of Great Portland-street, used to supply it, and I suppose does so still, as well as seaweed, &c. 1 kept a small aquarium for a long time near London some years ago, but I obtained the sea-water during trips to the seaside, using well-washed wine-bottles for its conveyance.-George Guyon, Ventnor, Isle of Wight.

QUERY ABOUT MICROSCOPES.-Would any one kindly oblige an inquirer with some information as to the relative merits or advantages of the various stages pertaining to Microscopes; viz., the plain sliding stage, the circular and rotating stage, the mechanical stage? Also as to "draw-tube," &c. I have a small French instrument (triplet), reputed to be 200 diameters, and am desirous of replacing it by something more serviceable and satisfactory (with coarse and fine adjustment, &c.); and as the instruments of different opticians are so various in manufacture and price, all the information I can gather seems to tend to confusion, and I meet with no friends and acquaintances who have any knowledge of microscopes whatever. Is it absolutely necessary to obtain the basis of a good instrument only by the expense of the mechanical stage, and other complicated apparatus? As to objectives, the author of "Half Hours" recommends in a general way the 1-inch and 14-inch. Would that apply to the second or third rate quality, or to the higher and more expensive glasses ?-Enquirer.

REPTILES AND THEIR YOUNG.-I was very much interested with Mr. Forskey's account of the alligator taking her young ones in her mouth and conveying them to a place of safety. Had we more of these observers of nature, I think we might get the question solved about our own reptile, the viper, as to whether it does the same thing. I can easily understand a five-feet alligator opening her capacious jaws and the young taking refuge there; but there is no comparison between a reptile of this size and a small

thing like the English viper, of 20 inches in length; for a reptile of this length to receive say six or nine young ones into its body, seems a stretch of the imagination when we consider that the young ones are generally about six inches long when bornnearly one-third the length of the parent. I hope that the ensuing summer will settle this question. If any observer should have the good fortune to see the swallowing operation, secure the reptile, and put it in a place of safety, and if the young should ever emerge into the light of day, we should then be satisfied as to the swallowing theory; till then I should say, well, it is not proven.-James Kirby.

ZOOLOGICAL STUDY.-Will you kindly insert the following ?-A society is at present being formed for the promotion of general Zoology, by means of collection of types, a library, and general investigations. The hearty co-operation of zoologists in the furtherance of the object is earnestly desired. A committee of management has been already formed. Further particulars may be obtained upon application to the Secretary, 4. J. R. Tunbridge, 2, Ashurst-street, Battersea.

MARINE AQUARIUM.-In reply to "J. G." I think the best thing he can do to obtain his supply of "salt-water" is to manufacture it himself, unless he can purchase any of Mr. Lloyd, of 20, Portlandstreet, Regent's Park, who used to sell it. If "J. G." is unable to obtain any, he had better make use of the following receipt.-Table-salt 3 ounces, Epsom-salt ounce, chloride of potassium 40 grains troy, chloride of magnesium 200 grains troy, to every gallon of water. With regard to the maintenance of the aquarium, if "J. G." will communicate with me, I shall be glad to give him every information.— J. T. T. Reed, Ryhope, Sunderland.

AN ORNITHOLOGICAL OPERA.-The Manchester Evening News, of February 17th, had the following paragraph copied from the Swiss Times:-" An extraordinary public entertainment has been produced in Lima, Peru, by an Italian named Contarini, who proposes to bring his exhibition to Europe. He has taught and trained, by dint of great patience and perseverance, an opera company, made up of thirty parrots and paroquets, who perform two of Bellini's operas, “Norma" and "Sonnambula,” on a miniature stage, with full chorus and recitative. The director and manager accompanies the artists on a piano harmonium, and the perfection with which each bird sings his part, and the excellence of the chorus, are prodigious. The début of his lyrico-ornithological company in "Norma" was attended by the wealth and fashion of Lima. When the paroquet that sang the contralto had finished the allegro to the "Salutation to the Moon," such was the enthusiasm, the shouting, and the applause at hearing a bird sing the "Casta Diva," that the bird company, affrighted, took flight, and sought refuge among the side scenes. This interrupted the performance for fully a quarter of an hour, and Signor Contarini had to tranquillize the "artists" by giving them bread soaked in wine, and henceforth the expressions of approbation were moderated, in order not to spoil the play. It appears that the bird artists have now become accustomed to the applause. The correctness and propriety with which they give certain parts of the opera are wonderful. The primo tenore possesses all the airs and graces of the school of Mario, and the ladies of Lima have named the prima donna, Patti." One does occasionally see some remarkable performances

of animals, from fleas to elephants, but they pale into insignificance beside the above account, which must surely be either a hoax or a skit upon some human operatic company.-Robert Holland.

ELECTRICITY. A friend of mine has a pony whose skin, when rubbed, emits electric light. When the finger-ends are rubbed smartly along the animal's back till they become hot, a stream of light accompanies them. I should mention that the pony is closely clipped. Darkness is of course necessary for the experiment. Has such a circumstance been commonly noticed?-George Roberts.

THE OLDEST TREES IN BRITAIN (p. 265, last vol.). -The Yew-tree mentioned by Evelyn as growing in the churchyard at Brabourne, Kent, has long since ceased to exist. The Cowthorpe Oak near Wetherby, Yorkshire, appears to have undergone very little change during the last hundred years. I have a beautiful water-colour drawing done by a lady from her own sketch of the oak in the summer of 1872, and on comparing it with the engraving in the "Silva." edition A.D. 1776, there is very little perceptible difference. At present the lower boughs are propped up and the trunk is hollow: this may have been the case in 1776, although not shown in the engraving. Dr. Hunter, in describing this veteran, says: "When compared to this, all other trees are but children of the forest." Humboldt, Mrs. Somerville, and Professor Balfour (probably upon the computation of Decandolle), estimate the age of the Brabourne Yew-tree at 3,000 years, whilst the age of a yew-tree at Heddon, Bucks, has been computed at 3,200 years; and that of the Cowthorpe Oak at 1,600 years. It is a singular fact that many of the largest yew-trees were formerly, or are at present, growing in churchyards, as at Brabourne, Gresford, Crowhurst, Fountains Abbey, &c. &c. Did the early Christians select the proximity of such trees for their churches and burial-grounds? If the computation as to their great age can be depended upon, such would appear to have been the case; and I shall be glad if any of your correspondents will express an opinion upon this subject.-Francis Brent.

THE LIVER (p. 238, last vol.).-There seems to be no inherent improbability in the proposed identification of the Liver with the emblem of St. John. It is, however, an error to suppose, with your correspondent, that the eagle was ever imagined to have been the actual companion of the apostle, either during his "mission [exile] in ths isle of Patmos," or at any other period of his career. Indeed, the evangelistic symbols (vid. Ezekiel i. 5, seq.) were not always at first assigned in precisely the same manner by early writers; and the eagle was finally attributed to St. John, because, as St. Jerome tells us, "Joannes quasi aquila ad superna volat, et ad ipsum Patrem pervenit, dicens: In principio erat Verbum, et Verbum erat apud Deum, et Deus erat Verbum." But the subject is, perhaps, rather out of place in the pages of SCIENCE-GOSSIP.-R. 4. Pryor.

DISAPPEARANCE OF COLIAS EDUSA.-"J. R. S. C." observes in the March number of SCIENCE-GOSSIP, that he did not observe a specimen of C. Edusa during the autumn of 1873 near Gravesend. I was staying then in the Isle of Wight, where it is usually plentiful, but only saw two specimens, one of which I captured, though I spent several days in searching the clover-fields. This shows that the scarcity of C. Edusa last autumn was not confined to North Kent.-C. G. Thomas.

NOTICES TO CORRESPONDENTS.

W. RANSON.-Matlock is the best place in Derbyshire for obtaining minerals, but not half of those sold there as coming from the neighbourhood, are of local origin.

T. C.-We received your post card inquiring as to the cost of the advertisement of the Butterfly raffle, but we must decline its insertion, as raffles are illegal!

W. S. O.-The season for the study of micro-fungi is just coming on, the first plants producing them being the Lesser Celandine (Ranunculus ficaria). You cannot do better than at once to procure Cooke's "Microscopical Fungi," published by Hardwicke, 192, Piccadilly.

L.-We only admit "Exchanges" gratis in the column devoted to them. A collection for sale would be charged as an advertisement.

J. B. S.-Your specimen is Hepatica triloba, a European, though not a British plant.

H. C. R.-The "Geological Magazine," edited by H. Woodward, F.R.S., is the only serial of the kind, published monthly at 1s. 6d., by Trübner & Co.

J. P. G.-Can you send us another specimen of the beetle ? The last was lost in transit.

M. J. G.-The empty eggs on the specimen of Sertularia are those of a species of Natica. The Ectocarpus is encrusted with diatoms, and the specimen from a cave at Tenby, and near Beaumaris, is Cellularia avicularia.

E. M.-Waterhouse's Cabinet List of British Coleoptera may be obtained from the author, British Museum. There are also lists (not for labelling) by Crotch, Rye, & Sharp.--G. C. B.

T. J. WOODROW.-You had best apply to the Hon. Secretary of the Geologists' Association, University College, Gower-street, for information respecting their meetings and excursions. That will be the society best calculated to meet your wishes.

R. O. S.-Your specimens are:-1. Diphasia pinaster; 2. Sertularia cupressina; 3. Corallina officinalis. The latter is a sea-weed, not a zoophyte.

PRESERVING ANIMALS, &c.-D. H. (Antrim) wishes to know the best way of obtaining the skeletons of animals otherwise than by placing the bodies near ants' nests. J. W. also asks for the title of some work giving instructions for collecting crustacea. Perhaps some of our readers will kindly answer their queries. The latter had best refer to SCIENCE-GOSSIP for June, 1872, article on "Collecting and Preserving" Lepidoptera, for entomological information. The vol. for 1872 further contains a lengthy article on "Collect. ing and Preserving " Coleoptera.

MISS H.-Some of your plants we can make out; others are too obscure and badly preserved. There are no numbers affixed to the specimens. The following are those named :Vinca minor, Diplotaxis murialis, Valerianella olitoria, Festuca uniglumis, Lagurus overtus, Ornithogalum umbellatum, Sherardia arvensis, in addition to common species of Galium, Lychnis, &c. Get Mrs. Lankester's "Wild Flowers worth Notice," London: Hardwicke, 192, Piccadilly.

W. D. E.-The insects which committed such ravages on your currant bushes are Nematus ventricosus (Gooseberry Saw-flv) common on both gooseberry and currant trees.G. C. B.

ERRATA.-In Mr. J. O. Harper's article on the Hemiptera last month, several important errors require correction. On page 53, for Trissiera read Trimere, for "trestle," read "bristle," and "stout" for "stone."

E. EVANS.-We are always happy to act as a mode of communication between subscribers. No charge is made for "Exchanges" if they do not exceed three lines in length.

EXCHANGES.

WELL-MOUNTED Slides of Stellate Scales from rare ferns; viz., Nothochlæna læris and Goniophlebium sepultum; also same in situ, for really good Slides.-J. Carpenter, Turners Hill, Cheshunt.

SECTIONS of Spinal Chord of Cat, Brain of Mouse mounted in balsam, for (mounted, named, and selected) Diatomaceæ.G. G., 11, North-terrace, Alexander-square, London, S.W.

EGGS of Kestrel, Sparrow-hawk, Curlew, Golden Plover, Dipper, common Tern, and others, for equally good Eggs. Unaccepted offers not answered.-Jas. Ingleby, Eavestone, Ripon.

GOOD specimens of Glyphomitrium Daviesii and Seligeria pusilla, for other scarce British Mosses.-Saml. A. Stewart, North-street, Belfast.

BRITISH Land, Fresh-water, and Marine Shells, for Foreign Land or Fresh-water.-G. Sherriff Tye, 58, Villa-road, Hands. worth, Staffordshire.

SLIDES of Arborescent Silver for Microscopic Slides.-F. G. Mellish, 32, Knowle-road, Brixton, London, S.W.

IMAGOS of Cynthia and Cecropia for Papæ of Machaon and Carpini.-S. H. Gaskell, Edgeley, Stockport.

SPIRACLE from larva of Geotrupes stercoraria and a dozen named species of Spiculæ, including Gorgonia, Alcyonium, Muricea, &c., well-mounted.-Send list to J. Wilson, Owen's College, Manchester.

SKIN of Thornback Skate (showing spines, &c.), with many other duplicates.-Send list to C. C. Underwood, 25, Gloucester place, Portman-square, London, W.

FOR Slide of Cholestrine, send stamped box and wellmounted Slide of Urinary Deposits to Wm. Sargant, jun., Caverswall, Stoke-on-Trent.

Good dried and pressed Specimens of Sea-weeds wanted for ornamental purposes.-J. Song, Regent-road, Salford.

LON. CAT., 38, 31, 68, 122, 204, 259, 261, 287, 1325, 1338, 1371, &c., for 3b, 11 vars., 12, 13, 36, 47, 50 vars., 56, 59, 60, 61, 62, 228*, 237b, 147, 148, 161, 676, &c.-John E. Robson, Seaview, Hartlepool.

BRITISH MOSSES wanted for Flowering Plants.-W. H. Pearson, Blue-Boar-court, Manchester.

WANTED, the Monthly Microscopical Journal (excepting vols. 1 and 2), for which 24 slides of choicely mounted Microscopic Objects will be given for each well-bound volume, or 18 slides for each 6 clean numbers.-Captain John Perry, 42, Spellow-lane, Liverpool.

WANTED, SCIENCE-GOSSIP (previous to 1870); 15 Microscopic Slides for good bound volumes, or 12 slides for each 12 numbers. Foreign gatherings of Diatomaceæ and Foraminifera will be given instead of slides if preferred.-Captain J. Perry, 42, Spellow-lane, Liverpool.

SECTIONS of Kidney injected two colours; ditto from human fœtus, and other anatomical preparations, for other really good slides, not diatoms or fungi. Lists exchanged.W. W. Jones, 14, Lancaster-street, Lancaster-gate, Hydepark.

TRANSVERSE section of Acer campestris, and skeleton leaf of Populus tremula, well mounted, for other good slides. Entomological subjects preferred.-E. Lovett, Holly Mount, Croydon.

SHELLS Wanted: Helix revelata, H. fusca, Achatina acicula, L. glutinosus, L. involutus. Offered: Clausilia dubia, H. sericea, Planorbis imbricatus, Planorbis lævis, and others. Exchange of Desiderata invited.-W. F. Sutton, Gosforth-grove, near Newcastle-upon-Tyne.

L. dispar, ulmata, brumata, hyperanthus, &c., for other species of Lepidoptera. Please send list of Duplicates.C. G. Thomas, The Grove, Highgate, N.

WANTED: H. obvoluta, H. lamellata, H. concinna, H. fusca. Offered: H. pulchella, H. rupestris, Pupa secale, C. lubrica, &c.-Miss F. M. Hele, Ellensleer, Redland-grove, Bristol.

COMMUNICATIONS RECEIVED UP TO THE 12TH ULT.-T. B. W. -A. T.-F. H. L-W. F. S-J. L-E. E.-J. E. R.—E. L.— C. M.-J. J.. H.-H. C. C.-A. M.-F. W. B.-F. K.-G. H, K. -T. B. W.-Dr. C. C. A.-S. J. McI.-C. M.-T. W.-F. M. H. -F. W. H.-H. M. W.-C. G. T.-C. L.-W. H. W.-R. H. M. -T. S.-M. L.-R. B.-W. F. S.-J. H.-G. W. B.-W. C.E. E. E.-C. C. U.-S. H. G.-W. S. jun.-E. L.-J. L. H.— W. F. D.-W. W. J.-W. H. P.-G. G.-J. W.-E. H.-S. A. S. -J. B.-J. G.-F. W. B.-Geo. G.-J. I.-J. C.-C. W.H. E. W.-T. W.-R. T.-E. E.-J. F. R.-R. H.-S. S. R.T. B.-G. S. T.-E. G. S.-C. C. U.-D. R.-H. A. M.J. H. G.-M. A.—A. G. R. T.-J. K.-J. F. F. R.-S. H. G.— C. P. H.-W. H.-H. G.-O. A.-S. A. N.-W. E. T.-T. T.— R. G. S.-A. T.-M. O.-T. B.-L. D. C.-J. P.—S. C. S.R. H.-&c.

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true that "there is nothing new under the sun," I am probably mistaken in supposing that the fact, to which I am about to draw attention, has not been published before. I need only say that I have not met with any mention of it, and I think it worth noticing.

Most people understand the principle of the stereoscope. They know that when Nature is looked at with both eyes, each eye sees a somewhat different view,-though from the way in which these views are combined, the difference is not generally recognized, and that, in order to give the true appearance of objects, receding and standing apart from each other (as viewed with both eyes), two different pictures must be taken, which must likewise be combined by means of lenses, as is done in the stereoscope; and when this is properly managed, the pictures no longer look like flat surfaces, but like the things themselves they are intended to represent, the objects all appearing to be in actual, bona fide relief.

That a great deal more is seen with two eyes than with one (when looking at things around) can easily be shown by simply holding up a finger at a span's length from the face, and at the same time looking at a small object behind it (such as a thimble) at a distance of a yard or two off. It will be found impossible to make the finger hide the thimble with both eyes open; but if one eye be No. 113.

Again, although a single painting-such as that of a statue in a niche in the wall-may be so well executed that, at a considerable distance, it is almost impossible to decide whether it is a statue or only the representation of one; and people have been deceived by such mural paintings when looking, for instance, from the boxes of a theatre to the walls opposite, under the influence of artificial light; still, there are no means at present known, or likely to be known, by which a single drawing (of landscape-scenery, shipping, buildings, and so forth, whatever its truthfulness or excellence) can be made to represent at a distance, say of from two to five feet, what would be seen with both eyes when looking upon the shipping, buildings, &c., or what would be seen when two stereoscopic pictures are combined: though a single drawing can, and often does, represent very exactly the scene presented to one eye by Nature. And the conclusion to be drawn from this is that the proper mode of looking at a drawing or picture, is to do so with one eye only; for, if looked at with both eyes, you can immediately detect that it is a mere picture on a flat surface (because, as before stated, there must then be two pictures to make a perfect deception), whereas if only one eye is used, and the head is held perfectly still, then (as the mind is precisely under the same circumstances as it would be if the real objects themselves were being looked at with one eye, and having no means of detecting any difference between the representation and the real things represented) at a short distance a drawing, after a few seconds, does almost seem to be stereoscopic, or, no longer appears as a mere flat surface and this is the point to which I wish to draw attention. The same reasoning will of course apply to photographs and good engravings, especially to those of buildings (such as the Forum

:

F

at Rome), cloisters, and interiors, and views of bare trees.

Whether the foregoing explanation accounts for the phenomenon or not, I think there can be no doubt that the pleasure of quietly and thoughtfully studying good drawings will be very greatly enhanced by the method I am advocating, viz., that of looking at them with one eye only.

I may mention to those who wish to try the experiment for themselves with the best effect, that Mr. Newman, of Soho-square, has a simple, useful, "handy "little instrument for the purpose, which greatly facilitates the process. Thurlow, Clapham, S.W.

ON PRESERVING AND MOUNTING FRESH-WATER ALGE.

HAVI

AVING had considerable experience in this matter, and having mounted many hundreds of slides which have retained much of their original beauty for many years, I may perhaps be able to give a useful hint or two to your correspondent interested in the subject. I have specimens mounted as early as 1851 which, though they have lost their green colour, still show the natural disposition of the endochrome, retain their external form unimpaired, and show no signs of intrusion of the varnish. The bulk of my slides are five or six years old, and the percentage of those which show any signs of "running in," or of evaporation of the liquid, is very trifling.

Such as are defective are nearly all my earlier attempts, and I firmly believe that slides mounted according to the plan I now adopt are practically permanent. Let us divide the subject into four heads; viz., forming the cells, fluid to be used, introduction of the plant, and sealing the cells. My plan is as follows:

:

1st. The Cell.-For most Algæ, including the Desmidiaceæ, a ring of thin gold size, spun by means of a "turntable."

This should not be narrow- inch is not too much; it should be either left to harden for several months or baked for a few hours in a slow oven.

For thicker Algæ, as Batrachosperms, Draparnaldiæ, &c., I prefer block-tin rings, which should be cemented to the glass by marine glue.

2nd. The Fluid.-I have tried nostrums innumerable without finding any which preserves the colour of these plants, and have come to the conclusion that we must be content if we can keep the endochrome in its natural form, sacrificing its colour.

Now if the medium be denser than the water with which the plant is filled, the endochrome is forced into the middle of the cell in a shapeless mass. It is essential to avoid this condition; and

after many experiments, I have adopted distilled water, slightly camphorated to prevent growth of fungi in the cell. If this medium be used, the endochrome usually retains its natural form and position.

3rd. Introduction of the Object.—Dr. Wood's mode of scouring the plants is inapplicable to any species with which I am acquainted. My own experience is that the specimen should be raised from the water in which it grows with as little disturbance as possible, placed at once in a drop of the medium in the cell, and, if necessary, slightly arranged by means of two needles. (The Desmidiaceæ require special treatment to obtain them quite clean, which I shall be happy to describe in another paper if desired, but which I pass for the present.) 4th. Sealing the Cell.-The most important part of the business.

The great secret of securing permanency is this: -Immediately before placing the object in the cell, put the latter on the turntable, and moisten the ring with the least possible dressing of fresh goldsize; touch the edge of the glass cover for about one-sixteenth of an inch inwards with the same substance.

Then lower the cover on to the cell. If there be a superfluity of the liquid, the fresh gold-size resists its escape, and the cover floats, as it were, on the medium. A gentle pressure then forces out the surplus liquid, and the last portions may be drawn out by a fragment of blotting-paper. No air enters, yet the medium is sucked out by the paper until the pressure of the air holds the cover on so tightly that it can scarcely be pushed on one side. The two surfaces of gold-size amalgamate without a particle of water remaining between or, in other words, neither cover nor cell is ever wetted.

Finally, two or three successive coats of goldsize are run round the edge of the cover at intervals of a few days, and the whole is secure. For a finish, I use a coating of copal-varnish, in which vermilion has been rubbed up with a palette knife; others prefer a similar preparation of white lead. It is most important to keep the slides flat in the cabinet; I believe the most carefully prepared specimen will give way in time if kept vertically.

While writing on this subject, may I remark that it is a great pity that this most interesting but complicated tribe of plants does not find some bibliographer who has time and ability to collate and reconcile the almost innumerable descriptions of genera and species now scattered through the works aud papers of Kützing, Braun, Thuret, Hassal, and a score of other observers at home and abroad, at present forming a heterogeneous mass of data, accessible to few, intelligible to fewer still, and requiring the patient labour of a master- hand during many years to reduce them to a harmonious scientific whole. A. W. WILLS.