abdomen travels but a short distance from the bee-burrows where she developed.

History of Hornia.--While the natural history of none of our N. A. species of Meloë has been traced or recorded, they will, beyond all doubt, be found to agree with their European congeners in their partial parasitism on Mason-bees. In examining the cells of Anthophora sponsa Smith, I have thus far failed to discover that Meloë is parasitic upon that species, but Meloë is in reality very rare around St. Louis. I have, however, found on four different occasions in the Fall, within the sealed cells of the bee mentioned, a very interesting and anomalous Meloid (Hornia minutipennis Riley), which may be taken to represent the typical partial parasitism of the family in the United States. There is a tendency in the family to wing reduction, but in no hitherto described species is the reduction carried to such extremes as in this (Plate 1, fig. 13) both sexes having the elytra as rudimentary as in the of the well-known European Glow-worm (Lampyris noctiluca). Another characteristic feature is its simple tarsal claws, which, together with the rudimentary wings and the heavy body, show it to be a degradational form. Anthophora sponsa, its host, builds mostly in steeply-inclined or perpendicular clay banks, and, in addition, extends a tube of clay from the entrance. The burrow of this bee has usually two branches which decline about an inch from the surface of the bank, and six or eight cells are arranged end to end. By means of saliva the inside of the cell is rendered impervious to the moisture of the honey and bee-bread stored in it for the young. It is evident that this clumsy Meloid will have difficulty in crawling out of or about the cells, and it is probably subterranean and seldom, if ever, leaves the bee gallery. The male can climb and drag his body, but with some difficulty, up a steep surface if rough, and, as he does not leave the bee-cell till spring, when the Anthophora tubes are very generally broken and have fallen, he may possibly wander a short distance from the mouth of the bee-burrow; but the female will naturally possess less power of locomotion. The triungulin is yet unknown, but the ultimate stage of the second larva as well as the coarctate larva, as shown by the distended and unruptured skins, exhibit the ordinary family characteristics, the legs and mouth-parts being atrophied in the former, and merely tuberculous in the latter. The lateral ridge, as found in

Epicauta and Meloë, is not conspicuous, and in this respect, as well as in the final transformations taking place within the two unrent skins, the insect approaches Sitaris. In the hairless and unarmed surface of the second larva, and of the third larva and pupa, as shown by careful examination of their shrunken exuviæ, the insect also resembles that genus.

[To be continued in May Number.]

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THE PREPARATION OF ROCKS AND FOSSILS FOR MICROSCOPICAL EXAMINATION.

IT

BY R. FRITZ-GAERTNER, PH.D.

T is often supposed by those who have never prepared sections of rocks or fossils that the process is associated with great difficulties and expenditure of time, but this in reality is not the case. A small amount of practice is needed for the beginner and he may soon be able to manufacture sections which are fit for the microscope. The time spent in the mechanical operation of grinding rocks is not only remunerated by interesting and instructive preparations, but adds also to a complete knowledge of their physical structure, gained by a close observation of the various features they present during the process of preparation.

In cases where large numbers of sections are to be prepared it is not possible for the lithologist or palæontologist for want of time to perform all the work himself: he may be assisted by any person of ordinary ability in the preliminary part of preparation. Those who do not personally wish to prepare sections can be referred to Mr. Fues, of Berlin, or to Mr. A. Julien, School of Mines, New York city, who prepare and deal in sections, which, on account of their perfection, deserve commendation.

In the present article I wish to describe the process of preparing rocks or fossils for microscopical study. They are mainly intended for those who design to make sections themselves, and to whom a detailed description of a mechanical operation may be of some assistance in their first attempts.

Selection of Rock Material.-It is quite important in order to make a complete microlithological analysis of rocks to select material which is characteristic. Most rocks are in various states

of alteration; it is therefore necessary to choose fragments both from the fresh and decomposed parts, as thin sections of the latter ones are just as important and instructive as those taken from parts in which no visible change has occurred. Usually such decomposed rocks are very fragile and crumbling, because their crystalline structure. or their cementing medium has been destroyed by the process of decomposition. Before undertaking to grind them their firmness must be restored. The fragments of such decomposed rocks are at first well dried and then placed in liquid Canada balsam, which is exposed on an iron plate to a gentle heat till it has filled and penetrated the pores and fissures of the rock. They are then separated from the Canada balsam and laid upon the warm iron plate till the balsam proves to be hard when cooled down, and are then capable of undergoing the process of slicing or grinding.

Apparatus. It consists in its most simple form of some plates of iron and glass about eighteen inches square, to allow a full stroke with the arm during the grinding process. They have to be perfectly even and flat. Emery of various degrees of fineness is required to be used on the plates with an addition of water. Fragments of rocks are ground by hand and treated as will be described in the following lines:

In the New York State Museum of Natural History at Albany, where a large number of rocks and fossils have to be cut and prepared for thin sections for illustrating the Paleontology of New York, the slow process of grinding by hand had to be abandoned, and a small boiler and steam engine of two and a-half horse power were purchased for the purpose of using steam-power for the grinding and slicing operations. The grinding apparatus is formed by two circular iron plates (A and B) of eighteen inches diameter and one-half inch thickness, which rotate horizontally with a velocity of about 300 revolutions a minute. The slicer which is used to cut the rock in certain directions, or to separate from it small slices to be ground afterwards, is a thin copper or steel disk of twelve inches diameter, and turns also horizontally with the same velocity as the grinding plates. For rocks above hardness 5, another slicer of steel is used, which turns vertically, and which is fed with diamond powder moistened with oil.

The whole apparatus may be run at the same time, and is

arranged in such a manner that no one operation interferes with another.

The grinding and slicing is performed by the aid of emery, which is constantly applied to the plates and slicer with a brush held in the left hand. The plates are kept wet by a small current of water. It is important to use emery of different but uniform degrees of fineness as the work progresses. A mistake usually made by beginners is to choose a too coarse emery, in order to hasten the work of grinding, but they soon discover that all their sections break and wear off long before being half finished. It is advisable to use for the coarse grinding on plate A an emery which can be bought in any drug store as emery No. 90 (A). Plate B is charged with flour of emery (B); it serves also to prepare one or two sorts of finer emery from it, by treating a certain quantity of the flour with water in a vessel which may be about three feet high and six inches in diameter. In stirring the water, the emery becomes suspended in it; after a lapse of fifteen minutes the water with emery which has not settled down during this time is decanted in a similar vessel and left there for twenty minutes more, when the water may be drained off. A sediment of fine emery will thus form in the latter vessel; and after having repeated the process for some time the emery sediment (emery C) is taken from the vessel, dried and bottled. Its degree of fineness is expressed by the number of minutes, which is in this case fifteen minutes.

Canada balsam serves as a cementing medium, it also is used to increase the transparency of various sections. It should be entirely clear and not of yellowish tint. Usually a solution of Canada balsam in turpentine is employed to mount such rocks as will not undergo any change in heating them gently over a warm plate of iron. For rocks which cannot be exposed to any heat, a solution of pure Canada balsam in chloroform is used. Both solutions of Canada balsam should be well bottled to prevent evaporation.

Object Glasses.-The slides of glass which are intended to bear the section should be entirely clear, free of any color, air bubbles or any other enclosures, as those which are used in other branches of microscopy. Their size should be uniform. Prof. Zirkel, of Leipzig, the distinguished lithologist, has proposed and introduced the following size, 45 mm. by 25 mm., which is preferable to the

ordinary 3 by 1 inch, as a slide 45 mm. by 25 mm. can be rotated on the table of the microscope; besides they are less liable to break in dropping them, and also take up less room.

In the New York State Museum of Natural History the slide measuring 45 mm. by 25 mm. is adopted. As it was found that this glass slide was too small for a number of sections of fossils, which exceed the usual size, two other standard sizes were introduced which are in proportion to the first. Size B is twice the size of first 50 mm. by 45 mm. Size C is twice the size of second 50 mm. by 9ɔ mm. It would be of great advantage if a

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uniform size was introduced in the various collections of those who prepare sections. The slide 45 mm. by 25 mm. is generally adopted with lithologists and paleontologists both in America and Europe.

Process of Slicing and Grinding.--The fossil or rock is at first marked with a pencil and afterwards with a file in the direction in which it is designed to be cut. It is then held with the right hand without any further apparatus, in such a direction that the revolving slicer will cut the specimen according to the marked line. The slicer is constantly supplied during the operation with flour of emery and water. If there is plenty of material and no special direction needed, small slices can be separated from the rock by a heavy blow with a hammer. The rock fragments should as a rule not be beyond the size of a twenty-five cent piece; of course it is of great advantage to prepare sections which offer a large field for observation, and the rock specimens should not be chosen too small, as they lose in size during the grinding process.

The slice of rock which has been separated either by the slicer or by the heavy blow with a hammer, is gently pressed with the right hand against the turning plate A, while the left hand supplies plate A with emery A and water. It is necessary to change constantly the position of the rock-slice in the right hand in order to grind it to an even and plain surface. The slice is then well rinsed and cleaned of any particle of emery A, and then transferred to plate B (emery B) where the grinding proceeds till its surface is free of any scratches Being cleaned of the emery B, it is brought upon glass plate C (emery C) and ground till its surface is entirely smooth. The rock section is finally well rinsed and brushed to clean off all impurities and allowed to dry.