little more historical arrangement, and if the visitor, in passing from one table or case to another, had been allowed to take the different classes of objects in something like their historical order, instead of jumping from new to old, and from old to new, until he lost all perception of the relations of the different classes to each other, he would, no doubt, have been benefited by it. Each class, too, might have been so arranged as to show the gradual development of the art which it represented. Thus, though we could not have started with art as it was cultivated by the uncivilized Britons, we might have traced it in its more barbaric form among the ancient Irish and the Anglo-Saxons, in the first development given to it by the earlier mediæval ecclesiastics, in the advance it made under the influence of Greece and Italy in the enamels, ivories, and illuminations of the twelfth and thirteenth centuries, till at length we come to the universal splendour of the renaissance.

It is curious to observe as we go on how slowly, and with what apparent difficulty, the purity of ancient art made itself felt in the mind of the medieval artist. The love of elaborate ingenuity and showy display which had characterized mediæval art at the earliest period predominated throughout, and was never more strongly apparent than in the works of the renaissance, however excellent the execution of the details may have been. Art, like costume, had become an affair of fashion, and not of pure taste, so that it varied in forms and character from year to year, and in this chiefly consists the historical interest of such a museum of objects of the later periods. And amid all this extensive display, we cannot help being struck with the. great absence of real beauty-it is all comparative, and in the whole collection we could select but few objects to recommend for imitation at the present day.

A SABELLA BUILDING ITS TUBE.

BY PHILIP HENRY GOSSE, F.R.S.

THE following particulars of a process of animal mechanics may possess interest for readers who study marine zoology under aquarian auspices, and I am not aware that they have been recorded before in detail. I give the ipsissima verba of my journal, written while the little mechanic was before my eyes. The account is an incidental testimony to the adequacy for aquarian purposes of the substitute for sea-water, the constituents of which I first made public in the Annals of Nat. Hist. for 1854::

June 30. My large tank of artificial sea-water, made in

August last, is now very rich in animal life. The stones and old shells are clothed with a woolly down of (probably) Ectocarpus, and the whole has the settled, old appearance of a natural pool bottom. Among the inhabitants is a Sabella, which answers in all particulars to Montagu's S. vesiculosa, except that it is much shorter than his specimen, being about one and a-half inches long, and its tube, at least the free part, about two inches. The dark purple vesicles which he mentions at the tip of the gill filaments, are in mine much more conspicuous than represented in his figure, that of the anterior filament on each side being much larger than the rest, and forming a stout, globose, nearly black ball; the others diminish to about the twelfth on each side, where they disappear. These balls are placed on the inner or upper face of the filament stem, at the point where the pectination ceases, the stem itself being continued to a slender point beyond it-the "short hyaline appendage" of Montagu. From their great resemblance to the tentacled eyes of the Gasteropod mollusca, I have little doubt that these are organs of vision. If so, the profusion with which the Sabella is furnished in this respect may account for its excessive vigilance, which is so great that not only will the intervention of any substance between it and the light cause it to retire, but very frequently it will dart back into its tube almost as soon as I enter the room, even while I am ten feet distant.

This morning I found my Sabella clean out of his tube, and lying on the muddy bottom below. I was afraid he was moribund; but he was actively wriggling, and his beautiful disk blossomed as widely as usual, though grovelling on the sand. Some six hours elapsed, when I perceived that his body was no longer naked, but enveloped in a new, loosely-constructed, but rather tightly-fitting tube, from the posterior part of which the naked tail was protruding, as yet unprotected. It was evident that the Sabella was meeting the emergency of his situation by forming a new dwelling, and that he had commenced, though unseen by me, by making a ring of mud cemented with a gummy secretion around the neck, which ring, as it increased in length, was continually pushed farther and farther downwards towards the tail.

The process of natural manufacture is always interesting. I removed my artificer from the tank, and put him alone into an ample cell of glass with parallel sides, giving him plenty of water, and a bottom of sand, on which I allowed to fall through the water a little clay, rubbed to a paste between my fingers in the water. As soon as the turbidity had a little subsided, so that I could use a lens, I had the gratification of seeing how he proceeded.

In order to make this intelligible, I must briefly describe the structure of the parts engaged. All that is ordinarily seen of the animal is a flower-like disk protruding from the tube. This disk is composed of two semicircular fans (the gills), the pair forming a complete circle, except that the points of junction, behind and in front, are marked by a slight opening. Each fan consists of twenty-one feathers, regularly radiating, and curling outwards with a beautiful turning-over of the tip, so that the whole disk bears the closest resemblance to a trumpet-shaped flower. The filaments, which I have called feathers, consist each of a slender stem, beset on the sides with two rows of beards (pinna), whose direction is upwards and outwards from the stem, so as to make a groove, of which the face of the stem is the bottom. The beards are in constant active motion, some being thrown inwards every instant, striking, and as it were feeling, the water, every one quite independently, moved by an impulse of its own. Under a high power (500 diam.) all the beards and the exterior face of the stem also, are seen to be clothed with minute, but rapidly vibrating, cilia.

In the centre of the flower-like disk is the mouth, which is guarded by a pair of little pointed tentacles, and on the outside of the disk, at the base, there runs round a thin, fleshy, very flexible collar of membrane, which, at the posterior opening of the fans, or that which is opposite to the two principal eyes, is produced into a pair of moveable, soft, tactile flaps, which turn outward, and hang over the edge of the tube in course of house building.

All this being premised, and the workman's tools being thus described, let us see how he works with them. Suppose him to be lying along on the bottom, near one corner of the square glass vessel, so that through one side a lens can be brought to bear on one side of the animal, and through the other on the disk.

We first glance at the disk, taking a front view of the creature. The filaments of the gill-fans are so active, bending inward and outward, and perpetually crossing one another, and the pinnæ are jerking hither and thither so incessantly, that we are for a while confused, and can make out nothing. We must fix our eye on some individual filament, and watch that, heedless of all the rest. Now we perceive that the tip of this is bent over outwardly, until the inner face of it is in contact with the bottom, the pinnæ expanding over the clay like the legs of the letter A. In an instant these close together, seizing, as with so many opposed fingers, a little of the soft and impalpable clay, and at the same instant the filament is straightened from its recurved condition, and we perceive a

minute pellet of clay lying between the pinnæ. The pellet takes a lengthened form, and presently glides quickly and equally along the groove of the pinnated filament towards the mouth, carried along by means of the cilia with which every part is clothed. Glancing at other filaments on each side, we see a similar pellet in each-at least, of those which, as the disk lies, are in contact with the bottom. As we follow the tiny mud pellets to their destination, we trace them to the mouth, where the two pointed tentacles stand guarding the entrance; these appear to guide the united pellets to the posterior orifice between the fans, through which we see the lump making its exit.

"We can learn nothing more of its progress from this point of view; but let us now direct our lens to the side of the animal. Here we again see the soft lump emerging between the fans, and as it progresses, the moveable fleshy flaps above described receive it, and guide it to the edge of the tube, plastering it as if with trowels on the edge, regulating its thickness, and smoothing it down. Meanwhile, the animal slowly revolves on its long axis, by which means all of the filaments in turn are brought within reach of the ground, and thus the labour of feeding the trowels is fairly distributed, and, also, the deposit is made in succession upon every part of the edge of the tube.

The tube increases in length by means of this process with considerable rapidity, and it is not long before the animal is once more completely protected. Probably, Probably, as the desertion of the old tube was in this case voluntary, it is not unreasonable to infer that the formation of a new habitation is normal, and takes place at certain, probably irregular, intervals, through life. There seems to be an inner layer of gummy matter secreted from the collar, on which the mud pellets are moulded; and often the lower portion of the tube-the first formed-is found in this genus of worms firmly adherent to a stone, and consisting almost wholly of this gummy matter without any mud coating. The substance, which hardens in water, and is insoluble, is of a horny texture and colour, a pellucid yellowish brown, and is probably composed of chitine. Perhaps in the case before me, if the animal had been reposing on a stone, instead of soft mud and sand, the first-formed portion of the tube would have been adherent.

I add Montagu's description (slightly condensed) of the species, the accuracy of which is proved by my specimen :Sabella vesiculosa. Body with many segments, pale, dull orange, minutely speckled with white. [gill fans] two, with about twenty-eight long ciliated fibres each, olive green, mottled with gray, partly in bands when

Tentacles

expanded; not forming a circle, but sub-convolute, the under part turning inward. At the points of each ray is a dark purplish vesicle, most conspicuous on the anterior ray of each plume, terminated by a short hyaline appendage. Mouth gaping; lips whitish, with two slender cirri; behind the tentacles a scolloped membrane surrounding the anterior end of the animal. Length six or seven inches. Tube coriaceous, but always coated with coarse sand and shells, ten or twelve inches in length."

DE CANDOLLE ON DARWIN'S THEORY.

THE Archives des Sciences has published some elaborate papers on the "Study of Species, on the occasion of a Revision of the Cupuliferæ," by M. Alphonse de Candolle; and in one, which appears in No. 60 of that journal, we find the following important remarks:

"I shall take this occasion to speak of the system of Mr. Charles Darwin, the most modern, and at the same time the most ingenious and complete, of the systems founded upon the evolutions of organized beings in the course of time.

"The progress of geology having demonstrated the antiquity of organized beings in terrestrial strata, and a succession of forms, according to sufficiently regular laws, it necessarily happened that the idea of a successive derivation of forms from other forms older than themselves should acquire new favour. The triumph of the system of the epigenesis† of organs conducted to it by analogy, and the recent experiments which have once more rolled back the theory of spontaneous generation, augmented the inevitable tendency of naturalists towards the doctrine of evolution. In fact, if we had been certain that inorganic bodies were transformed to-day and under our eyes into organized beings, it would appear quite plainly that at certain epochs, and even frequently, the same thing must have happened. But precisely the contrary is demonstrated, and it is therefore bable that formerly, as now, forms have been changed by evolution from forms which previously existed.

pro

"Cupulifera (cupula, a little cup, and fero, to bear) the nut tribe. A natural order of Dicotyledons."-Henslow's Dict. Bot. Terms. A wide significance must be given to the word nut.

"According to the doctrine of epigenesis no tissue, no organ pre-existed before its appearance; all are formed successively on the spot, and, so to speak, in all their parts. The individual nature of each animal rules and determines their composition and form. The theory of evolution, on the contrary, affirms that the germ contains in advance all the parts of the future being." Quatrefages' Metamorphoses de l'Homme et des Animaux, p. 52.