organisms, making manifest the periods of greatest fissional intensity; and also showing the result following on the cessation of fission. In the majority of cases it was an exhaustion of vital action and death; but in a certain proportion, in which fission was not so long continued, it was a rapid change to an amoeboid condition, resulting in the absorption or fusing of the lateral flagella with the body, and a change of form; the organism becoming now quite oval and having only an anterior flagellum. It swims easily, but has lost all the power and freedom of motion possessed before, moving only in a straight line. But it soon comes into contact with a colony of the organism in the springing condition, attaches itself to one of them, which then soon unanchors, and both swim away. In the course of time their movements become sluggish; the sarcode of the bodies is palpably blending, they become quite still, except for amoeboid movements, and then become one mass, oval in form, which elongates into a spindleshape, remaining motionless and still in all respects for three or four hours; when, as was ultimately and by long-continued effort made out, it pours out exquisitely minute, opaque, apparently round specks, which, when carefully and steadily followed with the best appliances, were seen to develop into the adult form and size.

The author then desired to discover the relative heat-resisting power of the perfect form, and the germ or spore. The adult forms were proved by a very direct method, which was fully detailed, to be wholly destroyed at a temperature of 142° Fahr. Two methods of heating were employed to test the resistance of the spore. One was the "dry" method which had been employed in the former researches; but which was somewhat modified and used with special precautions; and the result of an elaborate series of experiments proved, that by this mode of heating, the spore could resist a temperature of 250° Fahr.

It was next determined to test the heat resistance of the spores when they suffered the heat, diffused in a fluid. The difficulty of accomplishing this, so as to secure an unmistakable result, was carefully pointed out and dwelt on; and the opinion recently expressed by Dr. Bastian that it was "perfectly easy" shown to be an error.

The apparatus employed for the purpose was specially delicate, but enabled the author to test directly the results of heat on the spores as well as on the adult organism, without exposure after the vessel was once sealed. The form used was specially devised for these observations. The temperatures up to the boiling point of water were got in melted paraffin, and higher temperatures in a digester. The result was that 220° Fahr. was found to be the limit of temperature which the spore of this organism could endure without destruction of vitality. That is to say, 30° Fahr. lower than the same spores could bear in a "dry" heat. But it was pointed out, that to endure this temperature, implied protection of some kind; but that this in the undeveloping germ was not only capable of being understood, but would doubtless prove of immense value to the organism.*

*Nature,' No. 447, p. 102.

The Fine Adjustment of English Microscopes.-Many of the foreign writers on the microscope condemn the form of this adjustment, because they say that on account of the amplification constantly varying in consequence of the variation in the length of the tube, precise micrometric measurements are impossible. Dr. Van Heurck, the Belgian botanist and microscopist, writing in the Bulletin' on the new oil-immersion object-glass and the advantages it offers in dispensing with any correction adjustment, says, that it is curious that those who have thus criticised the fine adjustment should never have criticised the correction collar, for to that their objections particularly belong. By very precise experiments made with a cobweb micrometer, he satisfied himself that even with a the difference of amplification was insignificant, when with a Ross microscope the tube was lengthened or shortened to the full extent of the fine adjustment. With, however, anor, variations in the amplification of 100 diameters were obtained from the different positions of the correction from 0 dry to the extreme limit for immersion.

The Ornamental Colours of Daphniada.-A long and interesting paper on this subject by Dr. A. Weismann appears in Siebold and Kölliker's 'Zeitschrift,' vol. xxx. suppl. 123, illustrated with a plate in colours. Dr. Weismann, it will be remembered, originated some elaborate investigations into the "terrifying" colours of animals. The author thus summarizes the results of his researches:

1. Only a small number of Daphniade have variegated colours, which are for the most part developed in both sexes, seldom only in one, and partly in equal and partly in different degrees.

2. This colouring must be regarded as a decoration which was first acquired by one sex alone (probably for the most part by the males), but afterwards transferred in most cases to the other sex also. It is conceivable that this transfer was materially accelerated by the introduction of an alternating sexual selection, so that at the commencement of every sexual period, the males, at that time few in number, chose the most beautiful females, but towards the end of the sexual period the females made the selection from among the relatively

more numerous males.

3. The acquisition took place probably at a time when already a part of the year's breed multiplied only parthenogenetically. From the constant difference in colours between neighbouring colonies it may be concluded with some probability that the development of the colours only began after the isolation of the colonies, i. e. after the Glacial period in Northern Europe.

4. The transfer took place in a threefold direction, according to the law of homochronic transmission of Haeckel, modified by the gradual "retrogression of character,"-first to the other sex; secondly, towards the stage of growth when the sex is undeveloped, or at least full growth is not yet attained; and thirdly, to the parthenogenetically produced generations. In all three cases the different species which are provided with ornamental colouring are found in different stages, the highest stage, i. e. the perfect transfer of the colouring to both

sexes, all stages of growth, and all generations of the yearly cycle, is only obtained by one species (Latona).

5. The Daphniade furnish thus a further proof that secondary sexual characteristics may become general characteristics of species, and illustrate the Darwinian views of the origin of the colours of butterflies.

Schulze's Mode of Intercepting the Germinal Matter of the Air.Professor Tyndall contributes a paper on this subject to the Royal Society, of which the following is an extract:

In 1836, Schulze described an experiment which has obtained considerable celebrity. He placed in a flask a mixture of vegetable and animal matters and water. Through the cork two glass tubes passed air-tight, each being bent at a right angle above it. He boiled the infusion, and while steam issued from the two glass tubes he attached to each a group of Liebig's bulbs, one filled with solution of caustic potash and the other with concentrated sulphuric acid. Applying his mouth on the potash side he sucked air daily through the sulphuric acid into the flask. But though the process was continued from May till August no life appeared.

In this experiment, the germs diffused in the atmosphere are supposed to have been destroyed by the sulphuric acid, and doubtless this was the case. Other experimenters, however, in repeating the experiment of Schulze have failed to obtain his results. Schulze's success is perhaps in part to be ascribed to the purity of the air in which he worked; possibly also to extreme care in drawing the air into his flask; or it may be that the peculiar disposition of his experiment favoured him. Within the flask both glass tubes terminated immediately under the cork, so that the air entering by the one tube was immediately sucked into the other, thus failing to mix completely with the general air of the flask.

At a very moderate rate of transfer, I found, in 1869, that germs could pass unscathed through caustic potash and sulphuric acid in succession. To render the experiment secure, the air-bubbles must pass so slowly through the acid that the floating matter up to the very core of every bubble must come into contact with the surrounding liquid. It must of course touch the acid before it can be destroyed.

Reflecting on this experiment, and knowing that a sealed chamber simply wetted within suffices to detain the floating matter coming into contact with its interior surface, I thought that the same must hold good for the air-bubbles passing through a group of Liebig's bulbs. Every bubble, in fact, represents a closed chamber of infinitesimal size, and it seemed plain that if the walls of this chamber were formed of water instead of sulphuric acid, the floating matter would be effectually intercepted. This conclusion I verified by experiment.

Two large test tubes, each about two-thirds filled with turnip infusion, completely sterilized, were so connected together that air could be drawn through them in succession. Two narrow tubes passed through the cork of each test tube in the same manner as in Schulze's flask, and it was so arranged that the tube which delivered the air should end near the surface of the liquid, the exit tube in each case

ending immediately under the cork. Two series of Liebig's bulbs, charged with pure water, were attached to the two of this arrangement, one being connected with a large receiver of an air-pump and the other left open to the air. The connection between the receiver and the adjacent bulb being first cut off by a pinch-cock, the receiver was exhausted, and by carefully loosening the pinch-cock a very slow passage of the air through the test tubes was secured. The rate of transfer was, however, such, that the air above the infusions was renewed twenty or thirty times in twenty-four hours. At the end of twelve days the turnip juice was perfectly pellucid and free from life. Two days' exposure to ordinary air sufficed to render it muddy.

After twelve days the pinch-cock was opened so as to allow a momentary inrush of the external air, which was immediately checked by the reclosing of the cock. Three days afterwards the infusion of the test tube into which the air first entered was muddy and crowded with life. The contamination did not reach the second test tube. Similar experiments completely verify the conclusion, that in Schulze's experiment water may be substituted for sulphuric acid and caustic potash without any alteration in the result.*

The Ordinary Microscope as a Polariscope for Convergent Light.Professor A. de Lasaulx, of Breslau, describes in the 'Bulletin of the Belgian Microscopical Society' a method of using the microscope for this purpose. He points out that the ordinary polarizing instruments, whose magnifying power is always feeble, scarcely allow the examination by convergent light of small particles or the ordinary microscopic lamellæ of minerals requisite for the petrographic study of rocks, so that in the examination of very small crystals it becomes difficult to determine the parts most suitable for examination, or to grasp a number of optical details. For these observations, however, the ordinary microscope with two Nicol prisms is available-all that is necessary is to remove the eye-piece, and to work with the objective alone between two crossed Nicols. There is then so strongly convergent a light that the interference figures can be seen even in the thinnest plates. According to the dimensions of the plates under observation a high-power objective can be employed, but with the higher ones (as Nos. 7 and 9 of Hartnack) the field is not entirely round. This can, however, be corrected by applying to the lower Nicol two lenses, one of 12 mm. focus, and the other 6 mm., and so arranged that each of the two can be used separately or together, in the latter case giving a focus of about 5 mm. A completely round field is thus obtained even with the highest objectives.

By this method it is easy to see the phenomena of interference presented with convergent polarized light by crystals, which only become diaphanous when they are reduced to an excessive thinness. For instance, the figures of substances which exhibit rotatory polarization can be seen in thin plates cut perpendicularly to the vertical axis, as in cinnabar-also the black cross in the small scales of mica enclosed in the thin plates of certain basalts. The employment of

*Proc. Roy. Soc.,' No. 185.

the microscope as a polariscope is also specially advantageous for the study of small macled crystals of a structure more or less complicated and rich in interlacings, which only become visible with polarized light. With the eye-piece in place, these crystals can be examined with parallel light, and their peculiarities of structure and other points taken note of. The plates most suitable for examination can then be placed exactly in the centre of two crossed threads in the eye-piece, and on removing the latter, they can be examined with convergent polarized light. By this simple method the extremely complicated crystals of Phillipsite have been observed, also of Silesian Sirgwitz, which are only diaphanous when reduced to the thinnest plates. The small crystals of Tridymite were by these means shown by the author not to be hexagonal, as was considered from its pseudo-hexagonal form, with one optic axis, but biaxial— the two hyperbolas being plainly seen.*

Quekett Microscopical Club.-Professor Huxley, F.R.S., has been elected to the office of President of this club for the ensuing session.

Stromatopora as distinguished from Millepora.-Dr. Dawson, F.R.S., of Montreal, writes to the Annals of Nat. Hist.' (July) that the April number, containing Mr. Carter's paper, "Identity in Structure of Millepora alcicornis and Stromatopora," reached him not long after the completion of a series of careful microscopic studies of the Stromatopora and allied forms which abound in all the American limestone formations, and had arrived at the conclusion that these fossils appertain to the group of Rhizopods. After reading the paper, he re-examined the specimens of Millepora, but with the result of failing to find any indications whatever of the affinities asserted by Mr. Carter; and he gives the grounds for disputing what he terms "the somewhat extraordinary identification of two classes of organisms which scarcely resemble each other in anything except in being calcareous and porous."

Dr. Dawson mentions that having in his possession at present a considerable number of duplicate specimens of Stromatopora, in such a state of preservation as to show under the microscope their actual structure, he will be happy to send by post chippings of these specimens to any naturalists desirous of studying them and of comparing them with such organisms as Loftusia on the one hand or Eozoon on the other, with both of which the Stromatopora have decided affinities.

Professor Schwann's Jubilee.-The fortieth anniversary of the professoriate of the co-author with Schleiden of the "Cell theory," and author of Microscopical Investigations on the Identity in the Structure and Growth of Animals and Plants," was celebrated at Liége on June 23. The celebration included a laudatory oration of the Professor, the presentation of addresses from learned bodies throughout Europe, and of an album of living biologists, the unveiling of a bust, and, lastly, a banquet. Mr. F. M. Balfour, of Cambridge, represented England.

* Bulletin de la Société Belge de Microscopie,' vol. iv.

p. 177.