Lepidoptera (but not in Hymenopterous larvæ). We are thus led to suppose that it has something to do with the formation of the faceted eyes. If it has any relation with the bundle of fibres passing from the optic lobe, there is nothing to indicate it.

Secondly, the size of the olfactory lobe, with its olfactory bodies, correlated in insects with small antennæ entirely unfit for tasting, but on the contrary, with a very completely developed sense of smell, is in the author's opinion an excellent proof of the correctness of Leydig's view that the antennæ are organs of smell, whatever may be brought forward in opposition to it. If they are to be interpreted as an apparatus for detecting sounds, we, on the other hand, are acquainted with the finer structure of the organs of hearing in the Orthoptera, and know that they have no such constituted brain-centres as the olfactory lobes.

Thirdly, Flögel draws attention to the wonderful and so little understood facts that in insects, where the lobes ("bechers" of Flögel, "lappen," "gestielte körper," &c., of Dietl) and the substance around them (gerüst) constitute the greater part of the brain, there is indeed no connection of the nerve-fibres to be found with the remaining parts of the brain, and consequently also with the œsophageal commissures. The opinion that the ganglionic cells are in direct relation through fibres with the organs of the body is provisionally unfortunately contradicted. But where are the intermediate stations? he asks.

Finally, the author claims that the essay indicates the outlines of a future brain topography for insects, and shows that the single parts of the brain have their homologues in the different orders of insects; consequently a ground-plan in the organization is not to be mistaken, and thus a comparative anatomy of the brain of insects is outlined comparable with that of the vertebrates, as established by the researches of Stieda.*

The Movement of Microscopic Particles suspended in Liquids.-In Section A. (Mathematical and Physical) of the British Association's recent Meeting, the following paper, entitled 'Note on the Pedetic Action of Soap,' by Professor W. Stanley Jevons, was read:-"Since the publication in the Quarterly Journal of Science' for April, 1878, of my paper on Pedesis, or the so-called Brownian movement of microscopic particles, it has been suggested to me that soap would form a good critical substance for experiment in relation to this phenomenon. It is the opinion of Professor Barrett and some other physicists, that the movement is due to surface tension, whereas I believe that chemical and electromotive actions can alone explain the longcontinued and extraordinary motions exhibited by minute particles of almost all substances under proper conditions. Soap considerably reduces the tension of water in which it is dissolved, without much affecting (as is said) its electric conductibility. If, then, pedesis be due to surface-tension, we should expect the motion to be killed or much lessened when soap is added to water.

Having tried the experiment, I find that the result is of the

*American Naturalist,' vol. xii. p. 616.

opposite character to what Professor Barrett anticipated. With a solution of common soap the pedetic motion becomes considerably more marked than before. I have observed this result not only with china clay and some other silicates, but also with such comparatively inert substances as the red oxide of iron, chalk, and even the heavy powder of barium carbonate. The last-named substance, one of those which we should least expect to dance about of its own accord, gave a beautiful exhibition of the movement when mixed with a solution of about 1 per cent. of soap, and viewed with a magnifying power of 500 or 1000 diameters.

The correctness of this result was also tested by observing the suspending power of solutions of soap-solution compared with water. If a little china clay be diffused through common impure water, that, for instance, of the London Water Companies, the greater part of the clay will soon be seen to collect together in small flocks and fall to the bottom in two or three hours, the water being almost clear. However, if about 1 per cent. be dissolved in the water, the behaviour of the clay is quite different. The larger particles soon subside, but the smaller ones remain diffused through the liquid for a long time, giving it a milky appearance, quite different from the flocky and grainy appearance of the common water; if 1 per cent. of sodium carbonate be dissolved in common water, and china clay be mixed therewith, the subsidence of the clay is still more rapid, owing, as I have explained, to the increase in the electric conductivity of the fluid, and the consequent decrease of the pedesis. But I now find that if soap be added at the same time, pedesis is not destroyed, but considerably increased, and the clay remains a long time in suspension, two or three days at least.

These facts give a complete explanation of the detergent power of soap. It has long seemed to me unaccountable that for cleansing purposes the comparatively neutral soap should be better than the alkaline carbonate by itself; we are told that the alkali is but feebly combined with the stearic or other fatty acids. But why combine it at all if we need only the alkaline power of the base? The fact is, that the detergent action of soap is due to pedesis, by which minute particles are loosened and diffused through the water so as to be readily carried off. Pure rain or distilled water has a high cleansing power, because it produces pedesis in a high degree. The hardness of impure water arises from the vast decrease of pedesis due to the salts in solution. Hence the inferior cleansing power of such water. If alkaline salts be added, dissolved in water, it becomes capable of acting upon oleaginous matter, but the pedetic power is lessened, not increased. But if the soap be added also, we have the advantage both of the alkali dissolving power, and of the pedetic cleansing power. At the same time we have a clear explanation why silicate of soda is now largely used in making soap; for I have shown, in the paper referred to, that silicated soda is one of the few universal substances which increase the pedetic and suspensive power of water.

I believe that the detergent power of soap and water is one of

the many important phenomena which may be explained by the study of pedesis, and I propose to follow up the investigation of this movement in regard to the several substances which tend to increase it.”

The Preparation of Thin Sections of Objects of different Consistency. -In investigating the anatomy of corals Mr. G. von Koch, of Darmstadt found the calcareous skeleton one of the greatest drawbacks to his researches, as it often prevented any observations of the structure of these animals. Sections of decalcified pieces give good results only in special cases. Generally the decalcifying and still more the succeeding operations so disarrange the separate parts that their original relative positions can scarcely be recognized, and the structure of the calcareous parts is of course entirely lost. He applied the following method to overcome the difficulties, and obtained preparations that would show very clearly the structure, form, and position of the different elements. Pieces as small as possible of the object to be cut are stained thoroughly, and after rinsing, all water is got rid of by means of weak and afterwards proof alcohol. The pieces are then put in a cup filled with a very thin solution of copal in chloroform. (This is easily made as follows:-Pound the coarse pieces of broken copal in a mortar with fine sand, pour chloroform over the fine powder thus obtained, and filter the solution.) Then slowly evaporate the copal solution by putting the cup on a piece of pottery ware, which is warmed by a common night-light. The slower the evaporation the better. When the solution can be drawn up in threads which become brittle on cooling, the pieces are taken out of the cup, and laid for some days on the ware to harden quicker. When they have become so hard that the edge of the finger-nails makes no impression, cut the pieces into thin sections with a saw, and grind them smooth and flat on an ordinary sharpening stone. Then cement the plates by their smooth sides to a slide by means of Canada balsam or copal varnish, and lay them again on the warm plate. After some days, when the preparation has become firmly fixed, grind it first on a revolving grindstone (or a flat one), and then on a sharpening stone until the section has acquired the right thinness. Wash the section well with water and add Canada balsam, and cover with a covering glass.

If it is desired to show small quantities of organized substances in calcified tissues, the section is treated as above; but before the covering glass is put on it, it should be placed in chloroform till all the resin is drawn out, then carefully decalcified, and last of all coloured. The organic parts can be represented still more beautifully and without the least change of position if the section, as described above, is freed of resin, then cemented with very thick Canada balsam to a slide, and the exposed half only carefully decalcified, then washed and stained. By this means he succeeded in showing, for example, the most delicate connective-substance-lamellæ in the skeleton of Isis elongata.*

Measurement of the Dihedral Angles of Microscopic Crystals.— M. Em. Bertrand, whose paper on this subject, presented to the French

* Zoologischer Anzeiger,' vol. i. p. 36.

Academy, will be found at p. 217, has contributed some further remarks on the subject to the Bulletin of the Mineralogical Society of France,' of which the following is a translation, omitting those parts which repeat what has already appeared in the Comptes Rendus.'

"The eye-piece which enables the observer to make sure that one of the faces of the crystal has its projection perpendicular to the zero plane (described in the previous article), has been slightly modified with the view of obtaining greater sensibility. It is composed of a cylinder of flint of 6 centimetres long, to the middle of which is fixed, by Canada balsam, a plate of crown of the 4th of a millimetre thick. The flint having a greater, and the crown a smaller refractive index than that of the balsam, it will be seen that the upper part of the cylinder being placed at the focus of the upper lens of the eye-piece, two reticles will appear very close and parallel, and the interior of these two reticles will be illuminated if the face of the crystal has its projection perpendicular to the zero plane of the microscope. However little the crystal is turned to the right or left from this position, the part comprised between the two reticles will cease to be illuminated, whilst the exterior part will be more strongly illuminated either on the right or left according as the crystal has been turned.

The possible error is given by the value of the angle whose sine is al; this angle is less than 10', and as two readings can be made by turning the crystal to the right or left successively until the interval between the two reticles is completely darkened, the error is reduced to 5'.

Measurements made on crystals of to of a millimetre have given results correct within 6'.

The smaller the face of the crystal is, the greater, of course, will be the sensibility of the process. If a face is observed which is not very small, this face will reflect light into the microscope obliquely to the optic axis of the apparatus even when the projection of the face of the crystal on the horizontal plane is perpendicular to the zero plane, and this oblique light will destroy the clearness of the phenomenon; whilst if the face is very small, all the light reflected by it will be sensibly parallel to the zero plane of the microscope. Moreover, when the face of the crystal is not very large, its image is seen in the microscope on both sides of the double reticle when this face has its projection perpendicular to the zero plane; but on a slight rotation of the stage to one side or the other of the correct position, the image disappears either to the right or the left of the double reticle, and remains visible on one side only. This disappearance of one half of the image in conjunction with the extinction of the part comprised between the two reticles renders the observation very easy. It is sufficient therefore to employ magnifying powers proportionate to the size of the crystal, so that the sides of the face observed should appear in the microscope to be about 2 mm. difficulty in the use of high powers is their short focus, which prevents good illumination. Crystals of about 1 mm. may be measured, but for smaller ones the process ceases to be applicable."

The

M. Bertrand also explains his mode of illumination to be to place a luminous slit of about 30 centimetres long before the microscope

very exactly in the zero plane, which illuminates the crystal from the horizontal direction up to one of about 70°. By a mirror applied horizontally to the cube the crystal can be illuminated with the same slit by means of the reflected rays from the horizontal direction to one about 70° downwards. In this way there will always be a luminous point reflected by the crystal along the axis of the microscope, provided that the face of the crystal makes with the stage an angle between 10° and 80°, and as it is sufficient to measure two of the angles a, b, c, and two of the angles a, ß, y, the measurement will always be possible, for if the face of the crystal should make with one of the faces of the cube an angle less than 10° or greater than 80°, this face will make with two other faces of the cube an angle comprised between 10° and 80°.

The Microscope applied to the Phenomena of Double Refraction.In the same article M. Bertrand describes a method which he makes use of when greater sensibility is required than is obtained by the use of two crossed Nicols only. This consists of a thin plate made of four sections of quartz, alternately right and left handed, placed in the eye-piece of the microscope. This plate, of about 24 mm. in thickness, gives between the crossed Nicols a field slightly bluish and uniformly illuminated; but when a doubly refracting body is examined, the four sections present colours alternately blue and yellow, except in the position in which, by the ordinary method of observation, the field would be dark. In this latter case the sections remain uniformly illuminated, and of the same tint.

This method is, on the whole, much more sensitive than that of simple extinction, inasmuch as two different colours, illuminated and side by side, have to be compared; whilst when we have to estimate what is the position which gives the maximum extinction, two obscurities are compared, not by the side of each other, but one after the other. The same object can, however, be observed by the ordinary method of extinction and by that now described (using either the ordinary or the quartz eye-piece), and thus the results checked.

The Causes of Buzzing in Insects.-M. J. Perez is the author of the following:

"Since the experiments of Chabrier, Burmeister, Landois, &c., the buzzing of insects has been ascribed to the vibrations of the air rubbing against the edges of the stigmatic orifices of the thorax, under the action of the motor muscles of the wings. These latter organs play only a very small part in the phenomenon by modifying more or less the sound produced by the respiratory organs.

I have repeated all the experiments of these authors: they have not always given me the results stated, or I have thought it possible to draw from them a conclusion different from theirs.

1. It is quite true that by sticking together the wings of a fly (Sarcophaga carnaria) as Chabrier has done, we do not prevent the sound from being produced; but it is not the fact that the wings can thus be kept completely motionless. The flexibility of these organs enables them at their base, where free, to obey the contractions of