The vibrion is killed by the oxygen, and it is only when it is in bulk that it is transformed in presence of this gas into corpuscular germs, and that its virulence can perpetuate itself."

Compressed oxygen killing the adult vibrions, I have desired to know whether it would not also kill the germs by keeping up the compression at high tension for a longer time.

Conclusion: The action of oxygen compressed at a high tension and maintained for a long time, acts upon putrefied septic blood in the same way as a temperature of 150°. It destroys the vibrions and the germs in which the septicity of the liquid is inherent."*

Escape of small Animals from Aquaria.-The following simple method of preventing small animals which swim about in an aquarium being carried away with the water has been successfully employed in the zoological station of Naples. The water is conducted away, either by a tube proceeding from the bottom of the basin to the surface, or by a siphon having the end of discharge bent up again to the desired water-level. In order that the small animals may not be carried away by the stream flowing through the tube or the siphon, these latter are surrounded by a cylinder whose lower end is sunk into the sand covering the bottom, whilst the upper end projects above the surface of the water. By this means the water is filtered by the sand before it reaches the orifice of the tube which draws it off. As regards the width of the cylinder, it is to be remarked that with coarse sand and a weak stream it need not be large; on the other hand, the stronger the stream is, and the finer the sand, the larger ought the cylinder to be, to allow as much water to flow away as is introduced in the same time. In applying the siphon as above described, it is advisable not to let the end which draws off the water reach the bottom of the aquarium, as otherwise sand might be drawn up into the siphon, and possibly stop it up. It is sufficient if the inner arm reach to the level of the bend in the outer arm.t

A New Form of Micrometer.-In No. 37 of the Journal of the Quekett Microscopical Club,' Mr. G. J. Burch explains in detail the construction and use of a micrometer which he has devised, and which he claims to be easy to make and equal in accuracy to all other micrometers except the Cobweb.

The principle on which it is based, is the comparison of the reflection of a scale with the image of the object. It consists of a cap fitting over the eye-piece, containing a piece of neutral-tint glass (or looking glass, with the amalgam removed in the centre) set diagonally, so as to reflect to the eye the image of a scale which is carried by an arm ten inches long attached to the cap, the object being observed through the eye-piece in the usual way.

To adjust the scale so that it may read decimals of an inch, &c., it is moved on the arm nearer to, or further from the eye, till on adjusting the focus so that the apparent distance of the two images may * Comptes Rendus,' vol. lxxxvii. p. 117.

† Dr. Spengel in 'Zoologischer Auzeiger,' vol. i. p. 106.

coincide, every tenth division on the scale shall cover the roth or Tooth of the stage micrometer according to the power used.

The Nutrition of Insects.-"I undertook, in September 1877, a series of researches on the nutrition of invertebrate animals, especially insects. My studies bore on the gaseous exchanges with the atmosphere at different periods of metamorphosis.

I shall only call the attention of the Academy at present to the variations in the weight of the animal, above all, in the nymph or chrysalis state, in which the excreta are almost entirely gaseous.

If we trace a curve, taking for abscissæ the times, and for ordinates the weights, from the egg to the perfect state, we find :-

1. In the larval state the ordinates grow rapidly, to a maximum .which corresponds to the moment when the larva ceases to feed; the curve has the form of a sinusoid, with a few irregularities at the times of casting the skin; beyond the maximum the ordinates decrease, forming a descending branch of another sinusöid.

2. This curve continues during the early times of the nymph; but starting from the 'confirmed state' of M. Dufour, when, in the Lepidoptera and Diptera which I studied (Bombyx mori, Musca vomitoria, &c.), the weight is reduced to half the value which it had attained in the larva, the variations become much smaller, the curve is changed into a straight line slightly inclined to the axis which represents the times; the inclination always increases in the latter days of the nymph.

3. At the moment of escape, there is an abrupt diminution of weight by the loss of the envelopes. During the short state of immaturity there are rapid alternations of augmentation and diminution of weight. (Here follows a diagram of the curve.)

4. In the perfect state and when the animal is taking food, there ́are successive augmentations of weight, which may reach and surpass the maximum weight of the larva, and become almost triple what it was at the time of escape; there are, moreover, temporary variations of this weight, in different conditions of movement or repose, of light or darkness, &c. In the animal subjected to starvation from the time of escape, death supervenes after a loss of weight, which in different individuals belonging to the same species, is a sensibly constant fraction-among the Diptera about half the initial weight.

The investigations above mentioned as to the gaseous exchanges, allow of the explanation of the greater number of these facts, which throw light on the physiology of invertebrate animals."*

Parasites on a Diatom.-M. Guimard, a corresponding member of the Belgian Microscopical Society, communicated to the Society, at their July meeting, a circumstance that he observed in examining some diatoms, mostly consisting of Pinnularia, which he gathered at the seaside. He was astonished to see a great number of the diatoms covered by small bodies of a yellowish brown colour, and moving with great rapidity. With a No. 5 of Nachet they were seen to have * M. L. Joulin, in Comptes Rendus,' vol. lxxxvii. p. 334. VOL. I.

X

a rectangular body, and contained in their interior a yellowish brown matter, with globules of a deeper colour, and resembling the ordinary endochrome of the diatoms. At each of the four angles was a long hyaline arm, of great mobility. Seen in profile, the body presented the form of an elongated oval. M. Guimard, who considers them to be parasites, adds that they were endowed with extraordinary agility, and by means of their long and flexible appendages explored all the parts of the frustules. A woodcut accompanies the paper.*

Mode of Development of the Tentacles in Hydra.-Mr. Mereschkowsky recently expressed the opinion that the fundamental number of the organs in the Hydroids (that is the number which enters into the composition of all the other numbers) was not four, but two, arriving at this opinion partly from facts which had shown him that the appearance and sometimes the disappearance of the organs takes place so. that they appear or disappear simultaneously two at a time. Observations on the mode of production of the tentacles in Hydra vulgaris and H. oligactis, he considers, serve to confirm this opinion, and to establish a general law which governs the formation and the order of appearance of every organ in this class.

The order of the appearance of the tentacles he finds as the result of his observations (which extended to three complete pairs) to be this:

The first two appear at the same time and (what is especially remarkable) are arranged opposite to each other; the others also appear in pairs, and are also arranged opposite one another; they do not, however, appear together, the second tentacle of each pair always appears later than the first, and this retardation is much greater in the third pair than in the second.

This curious mode of appearance of the tentacles in the genus is, so far as known to the author, peculiar to it, and does not occur elsewhere among the Hydroida, in which we observe three types of development, viz.:-(1) Appearance in pairs; (2) Appearance by four at a time; and (3) Appearance of all the tentacles at once, as for example in Tubularia. This exceptional case would serve very well to explain the fact (which is also exceptional) that in Hydra we very often observe the number seven, which does not accord with the formula 2 x n that in general characterizes all the Colenterata. In fact, if the sixth tentacle does not appear until long after the fifth, we may expect that in the fourth pair of tentacles the seventh will appear earlier than the eighth, and that this last will be delayed much more than was the sixth. It is in this way that we find a variable number of tentacles in the different species of Hydra, sometimes six, seven, eight, or even more. It may well be supposed that the individual sometimes dies before having had time to acquire an eighth tentacle. But there is no reason for thinking that the number of tentacles in Hydra is subject to such variations that it cannot be governed by any law. We may easily see that the facts are subjected to a general law, although, owing to their great complexity, the law does not strike one at once,

* Bulletin de la Société Belge de Microscopie,' vol. iv. p. 304.

and can only be ascertained by carefully studying the genesis of the animals.*

Fluid Mounting.-At the April Meeting of the Microscopical Section of the Troy (U.S.) Scientific Association, the Rev. A. B. Hervey described a method, which he had recently devised. In his study of the Algae and Lichens he had been troubled, as others have been, by the difficulty of permanently mounting specimens while studying them, without waste of time or change of arrangements. Most of the methods of mounting either ruin such objects entirely or else require considerable time, care, and special appliances that are troublesome to a busy student, and therefore instructive specimens are lost. The objects may be transferred from water to Farrant's solution of gum and glycerine, and mounted without delay; but the structure is not well preserved, and air bubbles are likely to be obstinately present. The objects show best in distilled water, sea-water, camphor-water, &c.; and to mount them instantly and with uniform success he prepares cells of the gum and glycerine solution put on by means of the turn-table in the usual way. Having made cells of the required depth, and laid them aside until thoroughly dry, the inner half of the width of the cell is varnished on the turn-table with gold size, which is also allowed time to dry perfectly. Objects in water are arranged and covered in these cells with ease, and are ready after lying aside for a time varying from a few minutes to a few hours, to receive a coat of gold size or other varnish, the fluid that exudes from the cell in pressing down the cover-glass having dissolved enough of the gum cell to hold the cover in position. It has not been found that the cell is too much affected by the fluid; but if it should be so, the cell could be made of the usual cements, insoluble in water, and then coated with a thin layer of gum.† Influence of Temperature on the Optical Constants of Glass.-In an article in the American Journal of Science and Arts' (April), Mr. C. S. Hastings gives the results of some investigations which he has made on this subject. "The most surprising fact," he considers, "which these results point out is that the variation in dispersive power attending variation in temperature is relatively enormously greater than that of the refractive power, a fact which has, he believes, escaped attention heretofore. It could hardly have escaped unheeded, however, did not a singular relation obtain in the coefficients. The dispersive powers of three specimens of glass (flint, sp. gr. 3.554; do. sp. gr. 3.151; crown, sp. gr. 2.482) computed in the ordinary way, are as 9:8:6 nearly, while the coefficients in question are as 9:6:5 nearly; hence if this relation holds approximately for all optical glasses, as is probable, an achromatic combination good for one temperature is good for all others within moderate limits.

Protecting Cap for Focussing under Water.-This, which was described in M. M. J.,' vol. viii. p. 44, appears to have been recently re-invented, under the name of " Dudgeon's Submersion Cap."

* Ann. and Mag. Nat. Hist.,' ser. v. vol. ii. p. 251.

The American Naturalist,' vol. xii. p. 333.

The Optic Rod in the Crustacea and Annelida.-The following are the "conclusions of M. Joannes Chatin, in his article on this subject in the Annales des Sciences Naturelles' (Zoology), 6th series, vol. vii. p. 31:

"In attempting to sum up the principal results, we see that the optic rod of the Crustacea presents general characters which are constant in the whole class, and also arrangements either special or of variable importance which differ according to the types examined. This should suffice to show the danger of the method too often followed, and according to which the observation of a few insects may furnish results capable of being immediately extended to the whole of the Arthropoda.

Limited externally by the cornea,' terminating internally in the ganglion of the optic nerve, the rod presents two very distinct parts, of which the characters as well as the importance differ notably-the one, internal and more or less slender, deserves more especially the name of rod; the other, external, short and swollen, but of variable shape, is the cone.

It is needless to recall here the general characters of the latter, and the signification of the central line in which it has been attempted to show the analogue of the filament of Ritter; but as far as regards the rod, I insist particularly on the value which it is proper to attribute to its transversal striæ, which do not in any way indicate a contractile tunic, but are proper to the rod which may be separated into a certain number of disks thus marked out. This disposition establishes a close relationship between the optic rod of the Articulata, and the rod of the Vertebrata.*

Such is, in short, the structure of the rod in the generality of the class; if we go back to the different types studied, the principal forms which it there presents can easily be recalled. In Astacus, Squilla, Pagurus, Eupagurus, and Paguristes, rods are met with, whose constitution is really higher, as many details show. The Cypridina offer analogous dispositions, but seem, however, to tend towards a close histological simplification; this is particularly marked in Typton, and more clearly still in Lysianassa, where the rod shows no transversal striæ and the cellules of Semper are represented only by a dark spot, from an early period of development.

Notopterophorus and Caprella scarcely differ from the types last studied, but as much cannot be said of Epimeria, in which the organic degradation is marked in a considerable degree, and leads to extremely simple forms which in Lichomolgus become still more rudimentary.

This rapid outline reminds us of the manner in which the study of the Crustacea has led us progressively to more and more simple bacillary elements. Moreover, and without wishing to enter here into the discussion of the theories to which I allude, we know the important part which many contemporary zoologists accord to the existing too heterogeneous series of Worms, whose ensemble would constitute a kind of 'groupe de depart' allied by a close affinity to

It is known that the researches of Boll have recently confirmed my own observations.