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JUL 5

1910

MICROSCOPE OBJECTIVES.

REVISED PRICE LIST.

Ar the suggestion of Drs. Carpenter, Michael Foster, and other eminent Microscopists, Mr. HENRY CROUCH has, during the last two years, carried out a series of experiments, with the view of producing

MICROSCOPE OBJECTIVES

of the highest class, at a cost that will bring them within the reach of all Students of Natural History, &c., Professional or Amateur. As the result, ho is enabled to offer them at the following reduced prices :

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From the } in. to the } in, this series is fitted with a new Adjustment for covered and uncovered.

A new Illustrated Catalogue of Microscopes, &c., will be ready in a few days, and forwarded on receipt of Four Stamps.

HENRY CROUCH, 51, LONDON WALL, LONDON, E.C.

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THREE DOORS FROM LATE ADDRESS.

LONDON INTERNATIONAL EXHIBITION, 1851.—Two PRIZE MEDALS. LONDON INTERNATIONAL EXHIBITION, 1862.-Two PRIZE MEDALS. PARIS INTERNATIONAL EXHIBITION, 1867.—THE GOLD MEDAL.

THOMAS ROSS,

MANUFACTURER OF MICROSCOPES, TELESCOPES, PHOTO

GRAPHIC LENSES, etc., etc., etc., 7, WIGMORE STREET, CAVENDISH SQUARE, W. (REMOVED FROM FEATHERSTONE BUILDINGS, HOLBORN),

LONDON, Has the pleasure of announcing that he is now prepared to supply a second ANTERIOR ARRANGEMENT to his } in. and i in. Object Glasses, which, when substituted for the ordinary front combinations, convert them into

"IMMERSION OBJECTIVES, giving most brilliant definition. This addition, which is strongly recommended, thus enables the Microscopist to use these Powers either with or without water. The Price of the Immersion Arrangement for the fin. is £2; for

the ta in. £2.10s.

ROSS'S 4-INCH AND 5-INCH OBJECTIVES, For the Examination of large Specimens of Mineralogical, Botanical, and

Entomological Objects. These Low Powers, which have been constructed more particularly to use with ROSS'S TANK MICROSCOPE, are readily convertible into very convenient

ACHROMATIC POCKET LENSES, of 21 and 34 inches focus respectively, by screwing the Optical arrangement into a German-silver Pocket Frame, specially made for that purpose. Price of the Frame, 20s.

CATALOGUES FREE ON APPLICATION.

THE

MONTHLY MICROSCOPICAL JOURNAL.

JANUARY 1, 1870.

1.The Structure of the Scales of Certain Insects of the Order

Thysanura.

By S. J. McINTIRE, F.R.M.S.
(Read before the Royal MICROSCOPICAL SOCIETY, Nov. 10, 1869.)

PLATE XXXVII. SOME months ago I had the honour to submit a few observations to the Royal Microscopical Society respecting some insects belonging to the Thysanura, fam. Podurida-insects which deserve to be better known to microscopists than they hitherto have been, from the single interesting fact, one of many connected with them, that their scales are very beautiful microscopic obejcts. Since then certain views have been put forward relative to the structure of the scales of one of these creatures, Lepidocyrtus Curvicollis, which do not harmonize with my own, nor with those enunciated by the late Mr. Richard Beck, in whose published opinions I entirely concur. By the courtesy of Mr. Joseph Beck I was invited last April to inspect the drawings of Podura scales left by his brother, and on secing them I was agreeably surprised to find that our observations, though quite independent of each other, were upon the same insects. In the drawings, which are exceedingly beautiful, the so-called “ bead-like spherules,” to quote from the recent papers on the subject, which are forming at the present time a bone of contention, are beautifully depicted, and the conclusion one must come to, therefore, is that they were well known to Mr. Beck. It is strange, then, that so accurate an observer as he is known to have been should not have made public the new views respecting the

150

EXPLANATION OF PLATE XXXVII.
Fig. 1.-Scale of Lepisma Saccharina x about 150

Lepisma from Bombay X ,
Petrobius Maritimus X

250
Greenhouse Degeeria X 1500
Templetonia Nitida X 1500
Degeeria Domestica

1500 VOL. III."

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markings, and corrected his former statements, in which he distinctly asserts his belief that the scale is a corrugated structure, if he believed them to have any real existence as spherules. But, on the contrary, the latest expression of opinion by that authority which I heard him give, was to the effect that no alteration had taken place in his views with regard to the structure of the scale of Lepidocyrtus (Podura scale).

In making some notes, as a necessary supplement to the short paper I have already communicated on the scale-bearing Poduræ, I may be permitted, perhaps, to state, with some diffidence, the objections which seem in my mind to militate against the new theories : I say theories because I have heard two urged. The most formidable objection to the “ bead-like spherule” theory seems to me to be the fact, that all through the scales of insects, whether Lepidopterous or Coleopterous, so far as my knowledge extends, the markings are due to corrugations or wrinklings of one or both membranes of the scales. Now, if this plan of structure holds good so extensively in the Lepidoptera, Coleoptera, and Diptera, as I believe it does, I cannot help asking, “Why should not the same plan affect the Thysanura ?I think I shall presently be able to show, by comparisons, that it does, with certain modifications. The other theory is founded on the optical illusion of rows of beads which is often observable when two Lepidopterous scales of known striated structure lie across each other at any angle. A similar appearance and its cause is alluded to by Mr. Beck in his book on the Microscope, in treating of the scale of Lepisma Saccharina. It also is often seen, but I believe it is equally illusive, in solitary scales of certain foreign Lepidoptera, &c., where the strong longitudinal costæ are crossed at right angles by transverse corrugations. The theory which is advanced is to the effect, that the elongated beads," or “note of exclamation ” markings of the Podura scale, are due to striæ on opposite sides of the scale, crossing each other at an angle of about 17°. Against it I would only urge one objection, namely, that supposing this to be the true solution of the question, we ought to see the elongated beads forming patterns with regard to each other either of squares or rhombs; but they do not, as a glance at any of the scales the structure of which is disputed, will, I think, convince most observers. Therefore I am unable to accept this theory as containing the whole truth and its explanation.

Now what analogy is there between the scales of the Thysanura, especially Podura scales, and the scales of other insects ?

If we compare the scales of Lepisma Saccharina, the British species, with the species of Lepisma lately alluded to in “The Student' by Dr. Mann (as introduced from the East Indies into Natal, where its destructiveness is a great nuisance)-some specimens of which species I believe found their way from Bombay to the

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