of the epithelium-cells lining its crypts has convinced me, that they are not a pavement epithelium, in the sense of being squamous cells, but have an intermediate or transitional form between the columnar epithelium and the tesselated epithelium. In the Narwhal, again, the cells are cylindrical, as in so many mammals. so that I believe the Cetacea to offer no exception to the view that these cells are a secreting epithelium, and they doubtless elaborate a secretion for the nourishment of the foetus. From the fact that the utricular glands had a much greater calibre in my specimen than in the one belonging to Dr Thomson, one may infer that even after the crypts are fully developed the glands still play a part in foetal nutrition.

The foetus in my specimen had an almost uniformly purplish-grey colour, but with a patch of yellowish-white on the belly near the anus. The snout was rounded; the fissure of the mouth 11⁄2 inch long; eye-slit 4 inches behind the snout, and surrounded by a faint circle; ear orifice very minute, 3 inches behind the eye-slit; blow holes above and a little anterior to eye slit. Length of flipper 7 inches, its anterior edge 12 inches behind the snout. Funis was attached to the belly about midway between the anterior and posterior end of the foetus. A low, but distinct dorsal ridge, the rudiment of a dorsal fin, commenced a little in front of a point midway between tip of snout and end of tail, and extended backwards for between 10 and 11 inches along the middle line of back. It had a lighter greyish tint than the surrounding skin. Breadth of tail was 151⁄2 inches. In a profile view of the foetus a slight depression in the contour of the top of the head was seen in the region of the blow-holes. The foetus in utero differed therefore very materially in colour from such a half-grown specimen as Dr Fleming described*, in which the upper part of the body was a dusky black, the belly white, and numerous oblong spots extended horizontally along the sides; still more did it differ from old specimens, which have a whitish marbled colour. The presence of a dorsal ridge is also of interest, as the Narwhal is described as without a dorsal fin.

I availed myself of the opportunity of examining the dentition of the foetus. On May 20th, 1872, I described to the Society the

* Memoirs Wernerian Socy., 1811.

dentition of a foetal Narwhal 7 inches long, in which I found two dental papilla developed in the gum, on each side of the upper jaw, but the early stage of development of the foetus did not permit me to say whether the anterior or posterior denticle would have been the one to become the maxillary tusk, though I thought it probable that the more anterior would become the tusk.

The

In this much larger foetus the superior maxilla was 8 inches long. At the anterior end of each of these bones were two well marked sockets, one opening immediately behind the other. The anterior socket contained a cylindriform rudimentary tusk. posterior socket contained an aborted tooth inch long, and inch in its widest diameter. The hinder half of the aborted tooth was attenuated, and had several short irregular processes projecting from it; the anterior half was smooth and rounded. This tooth was inclosed in a distinct sac, formed of fibrous tissue, which, like the sac of the rudimentary tusk, was firmly united to the fibrous tissue of the gum. There can be no doubt, therefore, that I was right in my conjecture that the more anterior dental papilla becomes the tusk of the Narwhal.

3. Observations on the Zodiacal Light. By C. Michie Smith. Communicated by Professor Tait.

While engaged in cable work in the West Indies, I had, during the winter and early spring of 1875, a number of very favourable opportunities of examining the zodiacal light.

Before leaving this country I had, under the advice of Professor Tait, and with a note of recommendation from Professor Jenkin, applied to the Royal Society for the loan of a spectroscope, to make observations with during the voyage; but unfortunately I was unable to obtain one, and so had to content myself with a small pocket-spectroscope. On the outward voyage I did not notice the light at all till we got well to the south, near Cayenne, on the 8th of January; and, owing to the very bad weather we had about that time, I was not able to make any satisfactory observations till we were again somewhat farther north. The general appearance of the zodiacal light has been so often described, more or less faithfully, that I need not attempt any description of it here. I wish,

however, to mention one feature with which I was much struck, and which I have never seen remarked on-namely, that, on watching the western sky from sunset onwards, it is impossible to tell when the diffused sunlight ends and the zodiacal light begins till it becomes so dark that the form of the latter can be traced to a considerable altitude, when it is seen to be longer and narrower, and inclined to the vertical at a considerable angle. I am strongly inclined to believe that near the sun it is very much wider than at some distance from it, for I have very good reason to think that what by people generally would be taken as simply the last of the sunset glow is really due to the zodiacal light. This part, of course, can only be seen in places where the twilight is very short. The best time for making observations I found to be about two hours after sunset, when all traces of twilight had certainly disappeared, and consequently all risk of confusion with it was gone.

On January 31st, in lat. 8° N., long. 56° W., the light was very bright, and I made some spectroscopic observations. At two hours after sunset the light was visible for 90° from the horizon, and so bright was it towards the horizon that I was able to get a distinct spectrum. I first opened the slit very wide, when I observed a broad strip of light, nebulous at the extremities, with a distinct reddish tinge at the one end; then, by gradually closing the slit, I obtained a narrower but tolerably pure continuous spectrum, in which I could distinctly see reddish, orange, and greenish-blue, and on making comparison with the spectrum of a lamp (placed at the far end of the ship so as not to dazzle my eyes), I estimated that the spectrum extended from the red to past the position occupied by the F line in the solar spectrum. A large number of observations taken on other nights, whenever the circumstances were favourable, entirely confirmed these first observations. On several nights, and especially on February 27th, when off Ponce, in the Island of Puerto Rico, I observed the spectrum from a short time after sunset til long after the last traces of twilight had disappeared, but no change was noticeable after the spectrum had become so faint that the Fraunhofer lines could not be distinguished, except in the brightness of the spectrum, as I was still able to see colour distinctly, but no traces of any bright lines.

On February 26th and 27th I took a number of sextant measure

ments of the zodiacal light. These are, of course, only approximate, as the light has no definite boundary-lines, but gradually fades off at the borders. The measurements were made by the help of stars, as it was quite impossible to measure the light itself. On the 26th sunset was at about six o'clock, the light was very bright for 30° from the horizon, having at the horizon a breadth of about 25°, and at an altitude of 30° a breadth of about 20°. At 9 P.M. the light could be traced quite round to the eastern horizon, a phenomenon which I observed on several other occasions. At 10 P.M. the light was scarcely, if at all, visible. That this sudden. disappearance was not caused by any change in the atmospheric conditions was clearly shown by the undiminished brightness of the stars. On February 27th the breadth at the horizon was 30°, while at an altitude of 30° it was only about 20°. The centre of the band passed a little to the south of the Pleiades. I endeavoured, by means of the sextant, to measure the inclination of the band to the vertical. For this purpose I chose two bright stars near the centre of the band-one at a considerable altitude, the other close to the horizon; I then measured the angle between these and the angle between the upper one and the horizon; these angles were respectively 55° 30′ and 51°, giving the value of 31° 30′ for the inclination of the centre of the band to the vertical. I had unfortunately no access to star-charts, else I could have fixed the direction more accurately; but even these rough observations confirm the ordinary statement that the direction is slightly inclined to the ecliptic.

The spectroscope used was one of Mr Ladd's admirable small direct-vision spectroscopes, with five prisms and a single lens. Behind the slit is a small round hole, through which the light may be made to enter by opening the slit very wide, and which is very convenient for examining monochromatic light. With this instrument it is easy to see a number of the Fraunhofer lines on a tolerably clear moonlight night. And such an instrument, though in some respects inferior to a simple large prism and slit, will, I believe, be found very suitable for work such as that described above, especially when it has to be carried on on board a ship much given to rolling.

4. Note on the Volcanoes of the Hawaiian Islands. By J. W. Nichol, F.R.A.S. Communicated by Professor Tait.

The late Transit of Venus Expedition gave the writer some opportunities of visiting several islands of the Hawaiian Archipelago, some details of which may prove interesting.

They form a group of islands about 10 hours west longitude from Greenwich, and about 20° to 22° north of the equator, and differ in size from 10 miles long by 6 or 7 broad, to 90 miles by 60, which are about the dimensions of the most easterly and largest, viz., Hawaii (the Owyhee of Cook). The general lie of the islands is from north-west to south-east, those in the east displaying the most recent traces of volcanic activity. In the older or western portion the main mountain ranges run in the same direction as the islands, rising in many places to a height of 3000 to 4000 feet, and having lateral ridges branching off at right angles, with an occasional crater of oval shape thrown up at a distance from them, and evidently of more recent origin.

The putting up of a meridian mark on one of these ridges in the island of Oahu was attended with some difficulty, the narrow space along which one had to ride, sometimes not more than a yard or two wide, with precipitous descents of 500 to 1000 feet on either side, not rendering it comfortable to any one with weak

nerves.

The two most easterly islands, viz., Maui and Hawaii, although having their greatest length in the north-east and south-west directions, are composed only of mountains standing singly, and present no appearance of ranges. Maui, indeed, is nothing more than a couple of mountains joined by a very low neck of land, on the top of the eastermost of which (Mount Haleakala), at a height of 11,000 feet, is found one of the largest and most perfect extinct craters in the world, being some 10 miles in diameter, which unfortunately time would not admit of our visiting. The sides of Haleakala are not precipitous, and the general view from the sea is that of a huge hog-backed mountain. Traces of flows of lava so recent as to be quite black, and not covered with vegetation, are also seen coming down from what had been openings in its sides a short distance above the sea-level.

VOL. IX.