surface of the liquid. After about 13 or 14 litres of the argon had been condensed, the stopcock was closed, and the temperature was kept low for some minutes in order to establish a condition of equilibrium between the liquid and vapour. In the meantime, the connecting tubes were exhausted and two fractions of gas were taken off by lowering the mercury reservoirs, each fraction consisting of about 50 or 60 cubic cm. These fractions should contain the light gas. In a previous experiment of the same kind, a small fraction of the light gas had been separated, and was found to have the density 17-2. The pressure of the air was now allowed to rise, and the argon distilled away into a separate gas-holder. The white solid which had condensed in the upper portion of the bulb did not appear to evaporate quickly, and that portion which had separated in the liquid did not perceptibly diminish in amount. Towards the end, when almost all the air had boiled away, the last portions of the liquid evaporated slowly, and when the remaining liquid was only sufficient to cover the solid, the bulb was placed in connection with the Töpler pump, and the exhaustion continued until the liquid had entirely disappeared. Only the solid now remained, and the pressure of the gas in the apparatus was only a few millimetres. The bulb was now placed in connection with mercury gas-holders, and the reservoirs were lowered. The solid volatilised very slowly, and was collected in two fractions, each of about 70 or 80 cubic cm. Before the second fraction had been taken off, the air had entirely boiled away, and the jacketing tube had been removed. After about a minute, on wiping off the coating of snow with the finger, the solid was seen to melt, and volatilise into the gas-holder.

The first fraction of gas was mixed with oxygen, and sparked over soda. After removal of the oxygen with phosphorus it was introduced into a vacuum-tube, and the spectrum examined. It was characterised by a number of bright red lines, among which one was particularly brilliant, and a brilliant yellow line, while the green and the blue lines were numerous, but comparatively inconspicuous. The wave-length of the yellow line, measured by Mr. Baly, was 5849-6, with a second-order grating spectrum. It is, therefore, not identical with sodium, helium, or krypton, all of which equal it in intensity. The wave-lengths of these lines are as follows:—

The density of this gas, which we propose to name

66 neon "

(new), was next determined. A bulb of 32.35 cubic cm. capacity was filled with this sample of neon at 612.4 mm. pressure, and at a temperature of 19.92° it weighed 0.03184 gram.

This number approaches to what we had hoped to obtain. In order to bring neon into its position in the periodic table, a density of 10 or 11 is required. Assuming the density of argon to be 20, and that of pure neon 10, the sample contains 53.3 per cent. of the new gas. If the density of neon be taken as 11, there is 59.2 per cent. present in the sample. The fact that the density has decreased from 17.2 to 147 shows that there is a considerable likelihood that the gas can be further purified by fractionation.*

That this gas is a new one is sufficiently proved, not merely by the novelty of its spectrum and by its low density, but also by its behaviour in a vacuum-tube. Unlike helium, argon, and krypton, it is rapidly absorbed by the red-hot aluminium electrodes of a vacuumtube, and the appearance of the tube changes, as pressure falls, from fiery red to a most brilliant orange, which is seen in no other gas.

We now come to the gas obtained by the volatilisation of the white solid which remained after the liquid argon had boiled away.

When introduced into a vacuum-tube it showed a very complex spectrum, totally differing from that of argon, while resembling it in general character. With low dispersion it appeared to be a banded spectrum, but with a grating, single bright lines appear, about equidistant throughout the spectrum, the intermediate space being filled with many dim, yet well-defined lines. Mr. Baly has measured the bright lines, with the following results. The nearest argon lines, as measured by Mr. Crookes, are placed in brackets :

:

The red pair of argon lines were faintly visible in the spectrum. The density of this gas was determined with the following

*June 16th. After fractionation of the neon, the density of the lightest sample

had decreased to 137.

results-A globe of 32:35 c.c. capacity, filled at a pressure of 7650 mm., and at the temperature 17.43°, weighed 0-05442 gram. The density is therefore 19.87. A second determination, made after sparking, gave no different result. This density does not sensibly differ from that of argon.

Thinking that the gas might possibly prove to be diatomic, we proceeded to determine the ratio of specific heats :

Inasmuch as this gas differs very markedly from argon in its spectrum, and in its behaviour at low temperatures, it must be regarded as a distinct elementary substance, and we therefore propose for it the name "metargon." It would appear to hold the position towards argon that nickel does to cobalt, having approximately the same atomic weight, yet different properties.

It must have been observed that krypton does not appear during the investigation of the higher-boiling fraction of argon. This is probably due to two causes. In the first place, in order to prepare it, the manipulation of a volume of air of no less than 60,000 times the volume of the impure sample which we obtained was required; and in the second place, while metargon is a solid at the temperature of boiling air, krypton is probably a liquid, and more volatile at that temperature. It may also be noted that the air from which krypton has been obtained had been filtered, and so freed from metargon. A full account of the spectra of those gases will be published in due course by Mr. E. C. C. Baly.

"Summary of the principal Results obtained in a Study of the Development of the Tuatara (Sphenodon punctatum)." By ARTHUR DENDY, D.Sc., Professor of Biology in the Canterbury College, University of New Zealand. Communicated by Professor G. B. Howes, F.R.S. Received June 15,Read June 16, 1898.

Thanks to the most generous and freely rendered services of Mr. P. Henaghan, Principal Keeper of the Lighthouse on Stephen's Island in Cook Straits, I have lately obtained a very perfect series of Tuatara embryos, ranging in age from just before the appearance of the blastopore to about the time of hatching. I have classified these embryos in sixteen stages, and propose shortly to publish a general

account of the development with numerous illustrations. As, however, it will still take some time to complete the drawings and manuscript, it appears desirable to publish at once a short summary of the most interesting results obtained. The general development, as already stated by Thomas, conforms closely to that of other reptiles, but the following features seem to deserve special mention :

(1) The development occupies about thirteen months, the eggs being laid (on Stephen's Island) in November and hatched about midsummer of the year following. The last stages in the development, after about the first four months, occupy a much longer period than the earlier ones, so that, having reached an already very advanced stage, the development seems to be almost if not quite suspended during the winter months.

(2) The blastoderm spreads around the yolk at a very early date, and the embryo first appears as a cap-shaped mass of cells, the front end of which is elevated above the surrounding blastoderm as the head-fold, while the hinder and narrower end is formed by an undifferentiated mass of cells representing the primitive streak. The front part of the embryo is formed of epiblast and lower layer cells, and from the lowest of the latter the hypoblast is subsequently differentiated.

(3) In the primitive streak a distinct blastopore makes its appearance, which presently opens into the enteron below, forming a very distinct neurenteric canal which persists for some time.

(4) The notochord appears to be formed by a forward growth from the primitive streak in front of the blastopore, rather than by dif ferentiation of hypoblast cells in the mid-dorsal line of the enteron.

(5) At a very early date the front end of the embryo sinks into the yolk, pushing the subjacent blastoderm before it in such a manner that the latter forms a kind of amnion closely investing the head and the thoracic portion of the body. This "amnion," though very thin, becomes differentiated into inner somato pleuric and outer splanchnopleuric portions, but, at any rate for a long time, without any mesoblast.

(6) At a comparatively late stage in development the anterior end of the embryo, together with the somatopleuric layer of the "amnion," is withdrawn from the splanchnopleuric layer (which belongs really to the yolk sac), and thus the embryo comes to lie entirely above the yolk sac.

(7) In the hinder part of the embryo the amnion is formed by uprising folds of somatopleure meeting and fusing above the embryo, probably accompanied by a down sinking of the embryo. This process is continued backwards for some distance behind the embryo, forming a narrow canal which communicates in part with the cavity of the true amnion, and opens behind on the surface of the blasto

derm close to the sinus terminalis. The " posterior amniotic canal " thus formed is lined by epiblast, but it lies embedded in the mesoblast of the serous envelope which gradually splits off from the underlying yolk-sac around the embryo. The posterior amniotic canal arises at a very early date, and does not persist very long.

(8) The connection between the true amnion and serous envelope (false amnion) in the mid-dorsal line persists in part to a very late stage, but there is free communication between the two halves of the pleuroperitoneal space above the embryo.

(9) In connection with the vitelline circulation, very numerous absorbing vessels are developed which dip down far into the yolk, and large transparent globules of yolk, each surrounded by a layer of yolk "crystalloids," become arranged around these vessels like onions on strings. The yolk thus gradually assumes a very characteristic radially columnar structure.

(10) The parietal eye commences its development shortly after the appearance of the optic lobes. It arises by evagination of the roof of the brain in front of the prominence of the mid-brain, and is at first situated slightly to one side of the median line (the left side, so far as yet ascertained). It very soon becomes completely disconnected from its stalk as a closed, hollow vesicle, the wall of which is composed at first of a single layer of columnar cells. The outer (upper) part of the wall of the vesicle is thickened to form the lens and the inner (lower) part presently divides into two very distinct layers, and acquires a secondary, fibrous connection with the brain immediately in front of the stalk. It is a curious fact that while the parietal eye, after separating from its stalk, at first lies on the left side-the stalk itself is median.

(11) The posterior commissure arises just in front of the place where the stalk of the parietal eye connects with the brain and the stalk passes forwards above it. This fact seems to exclude the possibility of the stalk of the parietal eye representing the pineal gland, for, according to Balfour, the posterior commissure arises behind the pineal gland which is directed backwards.

(12) The pineal gland in Sphenodon appears to be represented by a mass of convoluted tubules lying in front of the stalk of the parietal eye.

(13) At a late stage of development (in embryos estimated at from four to eight months) the body and part of the head are marked with very distinct longitudinal stripes of white on a grey ground. This striping almost entirely disappears before hatching, being last retained on the under surface of the head. This observation is in close agreement with those of Eimer on the markings of mammals, &c.

(14) In embryos of the same age a patch of cornified epidermis