with the entrance tube of the pump, while the other had bored in it four holes into which the ends of the experimental tubes were pushed until the "shoulder" (see fig. 3) was firmly thrust against the indiarubber. All junctions were luted with viscid glycerine, and it was found that a good vacuum could then be produced and maintained for a considerable time.

In order conveniently to seal off the tubes they were again drawn out below the shoulder, so that when complete they had the shape given in the figure (fig. 3).

When atmospheres of special composition were required the mode of procedure was somewhat different; one of the four holes in the outer caoutchouc stopper was then appropriated to a gauge, formed of a straight piece of tubing of sufficient length, dipping under mercury: into another hole was fitted a glass tube to which was attached a piece of india-rubber tubing with a clamp. The pump was then worked until the gauge showed the required tension, when the gas was admitted from a small gasholder by attaching the stop-cock of the gasholder to the india-rubber tubing and opening the clamp.

The nitrogen used was prepared by removing the oxygen from atmospheric air, either by the prolonged action of alkaline solution of pyrogallic acid, or, in some instances, by the combustion of phosphorus; in the latter case the oxides of phosphorus were removed by agitating with solution of caustic potash.

Our oxygen was made by heating pure chlorate of potash alone in a tube of hard glass; lest any trace of ozone or chlorine should be present the gas was slowly bubbled through solution of iodide of potash; this precaution, however, appeared to be superfluous, the iodide solution remaining colourless.

Postscript. Received October 18, 1878.

The oxidation of hydrogen by light, demonstrated in the case of oxalic acid, naturally suggests an inquiry into the deportment of oxygen towards hydrogen in sunlight under other conditions.

We have not, for the present at least, an opportunity of examining this question in the detail which it demands, but we think that it may be of interest to append to our paper the following brief observations.

One of the best known facts in the chemistry of light is the combination effected between chlorine and hydrogen, and in their behaviour towards hydrogen under the influence of light the halogens form an interesting series. Thus, while chlorine and hydrogen unite explosively in sunlight, bromine and hydrogen are with difficulty, if at all, induced to combine, and iodine and hydrogen do not unite at all. Again, water may be decomposed with the aid of sunlight both by chlorine and by

* Cl2+ H2O = 2HCl + 0.

*

bromine, but not by iodine. Finally, while hydrochloric and hydrobromic acid in aqueous solution each resist decomposition when insolated in the presence of free oxygen, it is known that hydriodic acid under like conditions is rapidly destroyed. This destruction, according to our experiments, is promoted by all the rays, but is much less active behind red glass than behind blue. It occurs also, but more slowly, in the dark.

Here we appear to have a phenomenon analogous to the oxidation of the hydrogen of oxalic acid.

The question arises how far a preliminary dissociation of the constituent atoms of the molecule may influence the reaction. It has been clearly shown by M. Lemoine‡ that hydriodic acid gas is completely dissociated by light; but the same observer states that in aqueous solution no such dissociation in sunlight can be demonstrated—a fact observed also by M. Berthelot. It may be, however, that the phenomena of dissociation and oxidation under light may go on side by side, the presence of oxygen promoting the splitting of hydriodic acid by its determining affinity, In like manner it may be that in the decomposition of oxalic acid the oxygen plays a similar part, determining the dissociation of C2O4.H2, and replacing the dissociated radicle C2O. The analogy of chlorine, however, leads us to the belief that, in its relations to hydrogen under the influence of light, oxygen may be classed with that element; but the reactions above noted would seem to indicate that, under these conditions, its affinity for hydrogen is inferior to that of either chlorine or bromine.§

We would note also the following known reactions which occur in air and sunlight:

(1.) The decomposition of arsenamine with formation of water and deposition of arsenic.

(2.) The absorption of oxygen by and precipitation of sulphur from sulphuretted hydrogen;-reactions which, although occurring in the dark, are accelerated by sunlight.

V. "Note on the Influence exercised by Light on Organic Infusions." By JOHN TYNDALL, D.C.L., F.R.S., Professor of Natural Philosophy in the Royal Institution. Received December 17, 1878.

Early last June I took with me to the Alps 50 small hermetically sealed flasks containing infusion of cucumber, and 50 containing

* Br2+ H2O=2HBr +0.

† 2HI+0=I2+ H2O.

"Annales de Chim. et de Phys.,” [5], t. xi.

§ Under ordinary conditions the direct combination of oxygen and hydrogen gases does not occur in sunlight.

turnip infusion. Before sealing they had been boiled for five minutes in the laboratory of the Royal Institution. They were carefully packed in sawdust, but when unpacked the fragile sealed ends of about 20 of them were found broken off. Some of these injured flasks were empty, while others still retained their liquids. The 80 unbroken flasks were found pellucid, and they continued so throughout the summer. All the broken ones, on the other hand, which had retained their liquids, were turbid with organisms.

Shaking up the sawdust, which I knew must contain a considerable quantity of germinal matter, I snipped off the ends of a number of flasks in the air above the sawdust. Exposed to a temperature of 70° or 80° F., the contents of all these flasks became turbid in two or three days.

The experiment was repeated; and after the contaminated air had entered them, I exposed the flasks to strong sunshine for a whole summer's day; one batch, indeed, was thus exposed for several successive days. Placed in a room with a temperature of from 70° to 80° F., they all, without exception, became turbid with organisms.

Another batch of flasks, after having their sealed ends broken off, was infected by the water of a cascade derived from the melting of the mountain snows. They were afterwards exposed to a day's strong sunshine, and subsequently removed to the warm room. In three days they were thickly charged with organisms.

On the same day a number of flasks had their ends snipped off in the open air beside the cascade. They remained for weeks transparent, and doubtless continue so to the present hour.

I do not wish to offer these results as antagonistic to those so clearly described by Dr. Arthur Downes and Mr. Thomas Blunt, in the "Proceedings of the Royal Society," for December 6th, 1877.* Their observations are so definite that it is hardly possible to doubt their accuracy. But they noticed anomalies which it is desirable to clear up. On the 10th of July, for example, they found 9 hours' exposure to daylight, 34 hours of which only were hours of sunshine, sufficient to effect sterilization; while, on the 29th of July, "a very hot day, with much sunshine," 11 hours' exposure, "9 of which were true insolation," failed to produce the same effect. Such irregularities, coupled with the results above recorded, will, I trust, induce them to repeat their experiments, with the view of determining the true limits of the important action which those experiments reveal.

* Vol. xxvi, p. 488.

VOL. XXVIII.

VI. "On the Structure and Development of the Skull in the Lacertilia. Part I. On the Skull of the Common Lizards (Lacerta agilis, L. viridis, and Zootoca vivipara)." By W. K. PARKER, F.R.S. Received October 18, 1878.

(Abstract.)

The youngest, and therefore the most important, embryos that have been worked out in this present piece of research, were sent me, with those of the snake, by Dr. Max Braun, of Würzburg.

Other valuable specimens were the gifts of Professor T. Rupert Jones, F.R.S., and Professor Alfred H. Garrod, F.R.S.

The three species worked out are closely related, and two of them are native to this country: these familiar Sand Lizards are amongst the smallest, and yet the most highly specialized, types, to be found among the Reptilia.

This type may be taken as a sort of " norma," and by it all the other Lacertilia may be measured, as it were, when their height in the Reptilian scale is to be determined.

When such forms as Hatteria and the chamæleon are compared with a typical Lacertian, then we see how much there is that is generalized in those outlying species.

Putting together what I have learned as yet of the structure of the skull in the true Reptiles, and comparing what is seen in these coldblooded Sauropsida with what is seen in the hot-blooded bird, I have come to the conclusion that the common lizard is a culminating type.

The snake, the tortoise, and the crocodile, notwithstanding their own peculiar specializations, are yet more general in their nature than the nobler and higher kinds of lizards: this is especially shown by the number of characters that are, in the latter, in conformity with those of the bird.

And, indeed, with the high or Carinate bird; for the skull of the Ratita (ostrich and cassowary) does not undergo, in several things, so much metamorphosis as the skull of the typical lizard; for, as I showed long ago, these birds are not devoid of a Batrachian strain.

Of all the lizards known to me the chameleon is the lowest ; in some respects the Chelonians come nearer the higher Lacertilia than that bizarre type does. I have carefully worked out the skull in the adult and the ripe embryo of the common kind, and in the adult of the dwarf species.

In several things the lizard's skull is but little modified from that of the snake; this is especially seen in the nasal structure, its glands, and the bones of its floor; so largely illustrated in my last paper.

These things are not repeated in the Chelonia and crocodiles, nor do they exist in the chamæleon; but in many birds, especially the

66

'songsters," these curious specializations reappear, but the parts are lessened and modified.

Even many of those metamorphoses of the skull, which when I worked out that of the chick seemed to me to be peculiarly avian, and indeed not to be. found amongst the almost reptilian Ratitæ, now turn out to be lacertian also.

For instance, the separate cartilages that pad the "basi-pterygoid processes " of the skull and the pterygoid bones, at their articulation, these appear in the lizard; and even the division of the septum nasi from the ethmoidal wall begins in Lacerta, and other lizards.

That separation of the two regions has its explanation in the higher birds, whose fore face hinges on the skull; notably in the parrot.

In Lacerta it is a mere "fenestra," of no use to the creature; so it is in the semi-struthious Tinamou, and in some low, Southern passerine birds, e.g., Grallaria squamigera.

But in the huge Ratitæ it is as absent, as in the Chelonia, and the low chamæleon.

This latter kind has no column-shaped bone on the pterygoid ("epipterygoid"); that bone exists but is small and modified in the Chelonia; in birds, especially the "songsters," it is manifestly a process of the pterygoid, but I have never seen it as a distinct bone.

These are some of the more striking characters in the skull of the adult lizard and its sauropsidan relatives, namely, snakes, tortoises, crocodiles, and birds: the latter, it may be remarked, differ less in their structure from a lizard than many an imago-insect does from its pupa.

I have a strong suspicion that the serpent is degraded as well as more ancient and generalized, as compared to the lizard: it has manifestly lost its limbs, and the correlate of that loss is an arrest of the cartilaginous cranium. The small rudiments of orbitosphenoids and alisphenoids, seen in the snake, are no longer an anomaly and unexplainable: they are patches of the large tracts in the lizard, which has, contrary to what I long believed, a large alisphenoid on each side.

This part is not a continuous flap of cartilage: in the bird it is, but it always has a great fenestra in its middle, even in them; in the lizard it is multi-fenestrate-a mere basket-work of cartilage, feebly and partially ossified.

In its auditory structures the high Lacertian corresponds very closely with the tortoise and the crocodile, and these three kinds differ only in non-essentials from the bird.

The snake and the chamæleon lie below them all, but the chamæleon is lower than the snake, and has a worse ear than most frogs and toads. The lower jaw of the lizard and the nestling bird agree very closely. The remains of the hyoid and branchial arches are far more ichthyic in the lizard than in the bird.