carries also a second slide, parallel with, and at the back of the other, by means of which a slow adjustment is obtained by the action of a stout steel lever passing through a channel in the limb; the lever is acted upon by the ordinary micrometer screw in conjunction with a stiff steel spring. This arrangement permits of the milled head of the fine adjustment being placed in a most accessible position, on a step above the trunnions supporting the limb and body of the microscope, almost similar to the fine adjustment in the old Ross model. This simple fine adjustment, when in use, leaves the body of the instrument quite untouched, and therefore not liable to swerve; an evil of common occurrence in cases where the fine adjustment is attached to the body itself. The magnification of objects is not altered by a difference in the length of body, as is more or less the case when the fine adjustment is obtained by means of a cylinder sliding in the nozzle of the instrument, and the thickness of an uncovered object on the stage can be directly measured by means of a divided scale and vernier which can be attached to the limb at the edge of the fine focussing slide.

The most important feature of the Zentmayer stand consists in an improved method by which the tail-piece or stem carrying the mirror, sub-stage, with all illuminating apparatus, can be turned aside or swung on a tubular pivot (placed at the back of the stage), the centre of which is in a line in the optic axis intersecting the plane of the object on the stage, and consequently also in the focus of the object-glass.

The use of this swinging tail-piece arrangement enables condensing and other lenses for concentrating light to be used at any angle below or even above the stage if required, affording peculiar facilities for obtaining oblique illumination, and in the adaptation of appliances to be used for the purpose. For registering the angle at which an object is best observed there is a divided arc on the upper segment of the swinging stem.

With the usual form of microscope stand, in which a fixed stem supports the sub-stage, oblique light has to be obtained either by the use of separate reflecting prisms or admitting light through peripheral stops from the margin only of high-angled condensers. These necessarily come very close to the slide, and there is a difficulty in regulating the obliquity of deficient marginal rays. In the Zentmayer stand, however, with the use of the swinging arrangement, condensers and illuminators of long focus can be used with great advantage, and abundance of light is obtained with low-power objectglasses such as the 1 inch and 1 inch.

In order to get the best results for oblique illumination a very thin stage was found to be requisite; a simple mechanical stage, with concentric rotary movement, has therefore been designed specially for this instrument by Mr. Wenham, having only one movable plate in its construction, the rectangular directions of which are performed by two concentric milled heads, something similar to the well-known Turrel stage. This stage is supported by a conical stem, which passes through the tubular pivot of the swinging tail-piece

arrangement, and is clamped at the back of the instrument by a strong screw and nut. This stage can be readily removed from the instrument and replaced by any other form of object support to suit the special requirements of microscopists.

The idea of swinging the sub-stage and illuminators on the line of the object under observation is not a new one, several plans having been adopted from time to time by different microscopists to effect this. The most important was the subject of a patent more than twenty years ago, by Mr. Grubb, of Dublin, who fixed, exterior to the stage, a sector comprising nearly a semicircle, upon which the attachments for the illuminators were made to slide. The centre of the arc was set so as to be coincident with the object in focus on the stage. The Zentmayer system, however, of swinging the sub-stage is the most simple yet devised, and does not interfere with the stability or ordinary use of the instrument, for when the swinging bar is clamped in line the peculiarity at first sight is not readily observed, and the contrivance of this effective arrangement is very creditable to the ingenuity of Mr. Zentmayer.

Digestive Apparatus of Spiders.-M. F. Plateau has communicated papers on this subject to the Académie Royale of Belgium, in whose Transactions' they will be found, and in the Bulletin of the Société Belge de Microscopie,' January 31, 1878. He states that the dipneumonous spiders have the pharynx and oesophagus so narrow, that the juices of their prey penetrate the buccal intestine by capillarity; the dilatation of the suction organ driving them forward. When this organ contracts, the narrowness of the tube obstructs their return like a cork, and they are propelled into the middle intestine. In the first part of their course they are mixed with the pharyngeal secretion, which may have the properties of insect saliva, but no experiments have been made with it. From a mechanical point of view, the cæca of the middle cephalo-thoracic intestine only play a passive part; and if they serve as reservoirs, the liquids only enter them by the pressure occasioned by the suction organ. The cæcal secretion is not acid, and probably not analogous to gastric juice. It is an error to suppose the middle cephalo-thoracic intestine of spiders is analogous to the stomach of vertebrates. The principal digestion of albuminous, starchy, and fatty matter is effected by the energetic action of the liquid specially secreted by the abdominal gland, which is generally yellow, and containing fine granules, fat-globules, and epithelial cells, more or less intact. It is slightly acid. As with insects and decapod crustaceans, the acting ferment is evidently different from the pepsine of vertebrates, and an addition of a feeble trace of hydrochloric acid, instead of enlivening its action, completely stops it; but, like the pancreatic juice of vertebrates, certain salts, such as carbonate of soda, slightly promote it. This liquid rapidly transforms starch into glucose. The abdominal gland of the spider is not a liver, although its containing glycogen, together with its form, tend to the supposition. Its liquid does not exhibit the properties of bile, nor its colour with reagents. It rather resembles the pancreas of vertebrates, but the likeness is not perfect. The matters accumulating in the middle

intestine pass onwards through the action of the very thin muscular coat of this portion of the digestive tube, and probably also under that of the muscular columns. This mass divides and becomes surrounded with a thin envelope secreted by the epithelium of the intestine. The result is the production of solid excrements, which collect in the stercoral pouch. A chalky liquid secreted by the malpighian vessels also collects there, and exhibits innumerable corpuscles, extremely small, discoid, or spherical, grouped in pairs, and sometimes accompanied with microscopic crystals in rhomboidal tables. The secretion of these tubes is neutral and contains salts, amongst which is chloride of sodium. So far as can be judged, it does not contain uric acid, or urates, but it is easy to show the presence of guanine. The stercoral pouch is a reservoir collecting the residues of digestion, and the malpighian products. Its contents are expelled at considerably long intervals under the influence of its well-developed muscular coat. We must remember, finally, that the dipneumonous spiders can live for many months, that is to say, during the whole season of physiological activity, without food.

Hooked Spines on the " Root-fibres" of British Polyzoa.-In No. 72 (Zoology) of the 'Journal of the Linnean Society' Mr. C. W. Peach, A.L.S., writes in regard to Scrupocellaria scruposa, that although it is common and well known he is able to add a little to its history. Having received a specimen on a sponge (Halichondria panicea) from the Frith of Forth, and desiring to know how it moored itself to the soft body, he cut open the sponge, and found, as he thought, curious sponge-spicules, differing from all he had previously seen. On tearing it from the sponge, he saw that the "spicules were actually the "tubulous root-fibres" of the Scrupocellaria. Having hitherto considered these "root-fibres" as smooth, with a disk for adhesion to anything, at the lowest end, it was a new fact to find that they were armed with stout hooked spines where they were buried in the sponge, the points of the hooks bent towards the zoophyte, like the flukes of an anchor pointing towards the bow of a ship when the cable is stretched tight. These hooked spines are shaped like the thorn of a rose tree, and surround the " root-fibres" in a rather irregular manner, and when dragged out of the sponge hold in their grasp numbers of the sponge-spicules; this at once explained why these "root-fibres" were armed with hooks, and the points bent towards the zoophyte.

In another specimen from the same locality it was found that the spines, &c., were constant under similar circumstances. A specimen of Canda reptans, collected in Cornwall before 1849, on examination, showed similar hooked spines on the "root-fibres." In the hope of confirming this with a Scotch specimen, Canda reptans was got from Newhaven (N.B.), unfortunately not on a sponge, but on Flustra foliacea; here the hooks were absent; but the tips of the "rootfibres" were furnished with short radiating processes spread out at right angles, and from these short disk-like processes were inserted into the openings and body of the cells of the Flustra, thus giving & firm grip on this larger fan-shaped and firmer support, and enabling the zoophyte to ride safely in a storm.

Here, then, we have curious instances of things low (?) in the scale so well adapting themselves to changed circumstances as to secure their safety and preservation. In no works on British Zoophytes is there any notice of these hooks.

A New Postal Box for Slides.-A new form of box for sending slides by post has been suggested in America by Dr. R. H. Ward, and is said to have "proved successful beyond anything tried before," in saving the slides from injury. The arrangement consists generally in removing the racks, and lining the top, bottom, and end of the boxes with thick, soft cloth, and arranging folds of the cloth, glued or stitched in place, like a rack at each end of the box, so that a double thickness of the cloth shall extend between the slides from each end one inch towards the centre. It is described in detail in the American Naturalist' for February, and Hardwicke's 'ScienceGossip' for April.

A "New" Box for Microscopic Slides.--In the American Journal of Microscopy' for May, Dr. Carl Seiler suggests that the racks of the boxes for slides should slant at an angle of 130° to the bottom of the box, the inclined position of the slides then obviating, as is said, the difficulty there is in reading the labels when the slides are upright (as well as the difficulty in getting them out), or injury by their sliding over one another when flat. This plan was exhibited in England many years ago, but discarded on account of its inconveniences.

Apparatus for resolving Test Objects.—Mr. George Williams, of the Quekett Microscopical Club, has contrived an apparatus for facilitating the use of the small bull's-eye illuminator devised by Messrs. Powell and Lealand for the resolution of Amphipleura pellucida. That illuminator Mr. Williams points out operates successfully on those specimens only which happen to lie in the direction of the width of the slip or within very narrow limits of it, the rest of the specimens being, from their position, wholly unsuitable for examination. If the slide is turned by rotating the stage of the microscope, the length of the slide quickly interferes with and pushes aside the bull's-eye. To overcome this difficulty is the object of the apparatus, which consists of a tubular disk-holder 1 inch long and inch diameter, the top cut out so as to leave three equidistant 1-inch uprights (as slender as possible, so as not to obstruct the light), with small lips, upon which can rest parallel a disk of thin plate or crown glass on which the diatoms are mounted. The tips of the uprights are slightly inclined inwards, to spring lightly against and steady the disk to overcome the suction of immersion objectives. The disk-holder slides over a tube fixed to a brass plate with a central hole, which is attached by screws to the stage of the microscope. The bull's-eye condenser is attached to the stand, and either the disk-holder or the stage of the microscope can then be rotated to get any particular specimen into *position.* A further improvement has been suggested, by substi

VOL. I.

* English Mechanic,' vol. xxvii. p. 307.

tuting for the brass plate a Darker's revolving selenite stage, by means of which the disk-holder can be readily rotated.*

Terricolous Rhizopoda.-M. A. Schneider has presented through M. de Lacaze-Duthiers to the Academy of Sciences the following

note:

It is known that some rhizopods are able to live on land. De Greeff has described six or seven species-Amoeba terricola and Arcella arenaria amongst others. We have found these latter forms and ten others incontestably new, and all belonging to the group of Amœbæ furnished with a test. The test has more or less the form of an ovoid, sometimes drawn into a neck at one of its extremities, and nearly always compressed so as to present two distinct faces. It appears to be chitinous, sometimes thin and transparent, and figured with hexagons, areoles, circles, &c., sometimes thicker and coloured brown, and in a very common Arcella formed as if by an agglomeration of small grit. It has only one orifice smooth or indented, terminal or situated on one of the faces bevelled out to receive it.

The sarcode body of the interior, observed in a state of repose, is clear and homogeneous without granules in its lower third part, which encloses only the nucleus and two or three contractile vacuoles. At the limit of this lower third and the two upper thirds is seen a layer of fine yellowish granules spread out in a transversal plane. The two upper thirds are formed of a protoplasm more or less irregularly granulous, with or without foreign bodies in process of digestion.

The nucleus, always spherical, encloses one or many nucleoles. When the animal is active this distribution of its constituent elements is disturbed, and it is seen to emit by the orifice of its shell pseudopodia which resemble in their general features those of the amoeba, and whose length may reach to double that of the shell. To emit these pseudopodia the animal detaches itself more or less from the internal walls of its habitation, to which it only adheres at various points by protoplasmic filaments.

If the exterior conditions become unfavourable the rhizopods retract and encyst themselves. In the interior of the shell is then seen a regular sphere, in which all the elements of the structure of the animal are recognized, enclosed with foreign bodies.

A certain number of these expelled before the encystment may form a protecting barrier at the orifice of the shell. On adding a little water they are seen to break the frail envelope of their cyst and to resume possession of their quarters.

We have seen conjugation in the case of four of the species, and there is reason to believe that it occurs in all.

To this conjugation succeed cysts whose contents represent sometimes those of the two contractants; sometimes those of one only; each one then encysting for itself after an ephemeral union with the other.

These cysts of reproduction give spherules or spores, the evolution of which we have not yet followed, but which we hope to be able to

* English Mechanic,' vol. xxvii. p. 370.