minute as to be scarcely distinguishable, and so little selfdependant, that they never dispense with their supporting prothallium during the whole period of their existence, and the microscope will at once show their affinity to Funaria in the lax parenchymatous areolation and inflated calyptra. Again, Archidium and Pleuridium are equally approximated to Dicranella, while Phascum itself for which we retain the common P. acaulon Lin. as the type is equally close to Pottia among the Trichostomaceæ. HABITATS. Few localities are to be found where some moss or other is not to be met with. Even in our largest towns, a few yards of open ground, if neglected for a time, become covered with a crop of mosses originating from spores wafted on every breeze. Bryum argenteum and Ceratodon purpureus occupy the paths, though probably they do not bear fruit, and Tortula muralis takes possession of the bricks and their interstices on the garden walls. If we extend our walks to the commons around, we find the list of species considerably augmented, and old sandstone walls bear in addition Grimmia pulvinata, with several Tortulæ and Brya. A few mosses are littoral or affect the sea-coast, especially several species of Pottia, with Trichostomum crispulum, brachydontium and littorale, Tortula nitida and cuneifolia. Again, the chemical nature of the soil or rock materially influences the character of its inhabitants: some are almost confined to chalk, as Seligeria calcarea and paucifolia, Funaria calcarea, several Tortulæ, Weisia tortilis, Thuidium delicatulum and histricosum, &c.; while clay-fields support the various species of Phascum and Ephemerum. Sandstone has Campylostelium, Brachyodus, Tetrodontium, &c.; and granite, slate, or basalt each supports some peculiar species: to the first of these especially are the Andreæas attached. Bogs are rich in certain species, especially of Mniacea, with Hypnum cuspidatum, cordifolium, giganteum, fluitans, nitens, &c. Trees are occupied by various species of Orthotrichum, Zygodon, Cryphæa, and Leucodon-some preferring the smoothbarked willows, others the rougher oak and elder; and, again, some confine themselves to the parts near the ground-as Weisia truncicola, Leskea pulvinata and polycarpa, Anomodon viticulosus, &c. As we ascend the mountains, we soon find we have reached the head-quarters of the mosses-—the numerous streams and waterfalls, and the frequent mists that saturate the atmosphere with moisture, keep them growing continually, and frequently impress a marked feature on the landscape, for species of Polytrichum and Rhacomitrium frequently cover extensive areas, to the exclusion of all other forms. Again, certain species-and some of these, too, among the most elegant flourish luxuriantly in these elevated regions, which we should look for in vain at a lower level, as Splachnaces Conostomum, various species of Grimmia and Andreæa, Hypnum Halleri, callichroum, reflexum, &c.; thus everywhere covering the bare places of the earth with a verdant carpet ere yet Spring dare put forth her flowers-clasping in their tender arms the crumbling stone, and smoothing the scarred face and furrowed cheek of the time-worn tower, or clothing the decaying trees with a mantle of green of varied shades, transforming each into a garden where the observing eye may delight to trace a miniature resemblance to the pine-woods, aloes, yuccas, and sedums among higher plants. USES. The old writers delighted to attribute many uses to mosses, yet, except among the most primitive races, few of them minister directly to the wants of man; the Sphagnums alone form the first origin of peat, which is still largely consumed for fuel. Linnæus tells us that Polytrichum commune was used by the Laplanders for beds, and highly praises it for not harbouring insects or any infectious disease; and this plant is still used in the dales of the north of England for the manufacture of small brooms; Splachnum Wormskioldii also forms the wick for the simple lamp of the Eskimos. Yet although their services in human economy are so small, in that of Nature how great is their end! The bear lines his winter quarters with a thick bed of Polytrichum; the squirrel and dormouse, and whole tribes of birds, use Hypnums as material for their nests; and if we shake a tuft of moss over paper, we shall find that it harbours a population we little dreamed of elegant little mollusca feeding among the branches, with tiny beetles and poduræ and curious acari hiding at the roots. Again, mosses have been termed the pioneers of vegetation, for, being able to establish themselves where little else can maintain a footing, they penetrate with their slender radicles the smallest crevices, and slowly disintegrate the substratum on which they grow, constantly arresting by their interwoven. tufts the dust-grains wafted on every breeze, and ever decaying below, ever extending above, they are slowly but surely accumulating material capable of supporting a higher order of vegetation. Their vital functions, too, must not be overlooked, for their myriad cells are for ever condensing the moisture of the atmosphere and adding their tribute to every mountain rill, which, borne onward to the ocean, is again returned to them in the mists and snow-wreaths that are their constant attendants. In winter and early spring they contribute much to the verdant covering of the earth, and to the supply of oxygen afterwards given out by the leaves of higher plants. I have mentioned the vast number of species that people our moss world, all unsurpassed in beauty of structure by any other group; and these are but a fragment of the Creator's handiwork, unnoticed and uncared for by the ordinary passer-by; yet, though yielding neither sustenance for the hungry nor medicine for the sick, there are times when their study will supply both food and physic to the mind. EXPLANATION OF PLATE LXXVII. a. Funaria hygrometrica, nat. size. 1. Spores. 2. Prothallium and young plants. 3. Male flower. 4. Antheridia and paraphyses. 5. Antheridium discharging spermatozoids, with one of the latter very highly magnified. 6. Fertilised archegonium. 7. Young fruit with vaginula. 8. Calyptra. 9. Perfect fruit before the fall of the lid. 10. One of the stomata from neck of same. 11. Portion of the annulus. 12. Longitudinal section through the fully-formed green fruit, showing the small sporangium, nearly filled by the columella. 13. Peristome. 14. A single tooth of outer and of inner peristome, with the central cribrose disc. 15. A leaf, with the cells constituting its areolation. 379 THEORY OF A NERVOUS ETHER. N my course of experimental lectures on medical science fication of the old and well-nigh obsolete theory of the existence of a nervous fluid; and I have since reduced to some form, in a published lecture, the ideas I wished to set forth.* It has been curious to me to observe the different lights in which this effort has been viewed by men of different phases of thought and knowledge. Some physicists have accepted that the theory suggests the existence of an intermediate agency between the matter of living bodies and the forces by which the matter is moved an agency essential to the correct understanding of the relations coexisting between the living matter and force. Others have thought the theory obscure and retrogressive, a kind of retreat into the bosom of Van Helmont, and of those fanciful heroes of Lord Lytton, who, still professing Helmontism as an article of scientific, and I had almost said moral faith, proclaim life to be "a gas." Lastly, certain enthusiastic writers, and, as they call themselves, experimenters, have actually laid hold of the theory to support modern spiritualism, and its idola of the theatre. To commence with the last of these critics, I need scarcely say, in relation to them, that there is nothing in my mind bearing in the remotest degree on their arguments. I speak only of a veritable material agent, refined, it may be, to the world at large, but actual and substantial: an agent having quality of weight and of volume; an agent susceptible of chemical combination, and thereby of change of physical state and condition; an agent passive in its action, moved always, that is to say, by influences apart from itself, obeying other influences; an agent possessing no initiative power, no vis, or energia naturæ, but still playing a most important, if not a • Medical Times and Gazette, May 6, 1871. primary part in the production of the phenomena resulting from the action of the energia upon visible matter. In respect to those who imagine that the theory of the existence of a nervous ether tends to materialise the phenomena of life and of living action, the answer is simple. The theory treats of an assumed material part of the living organism, and has no reference whatever to that more distant or spiritual essence of our nature of which, as yet, no more is known, physically, than of the energia naturæ itself. We must all accept that the impulses of men and animals, the volitions, the sympathies, the passions, are manifested by and through the material organism, the matter as a mechanism obeying the force that moves it. The tongue of man that speaks, the hand that gives, takes, strikes, aids, begs; the feet that make progression, and all parts that act, act positively as mechanisms of material character. How they act, in obedience to the impulses that move them, becomes, consequently, a distinct question that may be studied apart from the impulses themselves, and in the theory this is implied. The impulses, I mean, are considered as initial and independent motions, the origin of which forms no part whatever of the theory of a nerVous ether. Of the first order of critics, they alone appreciate the meaning I would attach to the theory of a nervous or animal ether. The idea attempted to be conveyed by the theory is that between the molecules of the matter, solid or fluid, of which the nervous organisms and indeed of which all the organic parts of the body are composed, there exists a refined subtle medium, vaporous or gaseous, which holds the molecules in a condition for motion upon each other, and for arrangement and rearrangement of form; a medium by and through which all motion is conveyed; by and through which the one organ or part of the body is held in communion with the other parts and by and through which the outer living world communicates with the living man: a medium which, being present, enables the phenomena of life to be demonstrated, and which, being universally absent, leaves the body actually dead-in such condition, i.e. that it cannot, by any phenomenon of motion, prove itself to be alive. I hope I have now made clear what is generally meant by the theory of a nervous ether. But there are yet two other points on which it is essential, for a moment, to dwell. In using the word ether I do not necessarily convey the common idea of a body belonging to the chemical family or group called the ethers, or the ethyl series. I use the word ether in its general sense, as meaning a very light vaporous or gaseous matter: I use it, in short, as the astronomer uses it when he speaks of the ether of space, by which he means a subtle but |