Mantle (biology)

“ This beautiful little creature, Cypræa Europæa, carrying its porcelain-like dwelling on its back, is enabled to move steadily along by the action of its single foot. When in action, the mantle, as it is termed, which is the general covering of the body, is greatly distended, and protrudes from the shell, which it perfectly encloses, folding up at the sides, and meeting at the top, the joining being scarcely perceptible, and the whole surface fitting so tightly to the shell, that the little ribbings are seen distinctly through it. ”

“ During life, this shelly plate is imbedded in the substance of the skin of the back, a thin layer of which clothes it; so thin that it can be very readily seen and felt notwithstanding. The mantle is much developed, forming two great irregular wing-like lobes, which stand up on each side of the body, and at pleasure either arch over the gill-shield, or are depressed, and widely expose it. ”

“ The mantle during life performs regular respiratory movements by which water is drawn into the cavity, passing between mantle and funnel, and is expelled through the funnel. In swimming the short arms are directed forwards, the fins undulate, and the motion is slow and deliberate; but if the animal is threatened or alarmed it swims suddenly and rapidly backwards by expelling water forcibly from the mantle cavity through the funnel, at the same time expelling a cloud of ink from its ink-sac. ”

“ Then Nature’s pure mantle would be seen slowly to disappear, the low grounds would be inundated with the snow-waters, the warm breezes would dry the mountain ridges, and with the first appearance of verdure joy would cause every heart to bound. ”

“ Concentration of Eyes in Special Parts of the Mantle.—Sharp has shown [295] that in several species of Ostrea, Cardium, Anomia, Lima, Avicula, Arca, and Tellina pigmented cells, with a highly refractive cuticle, are scattered over a considerable portion of the mantle. Experiment has proved the powers of ‘vision,’ i.e. of sensitiveness to different degrees of light, possessed by these organs. In Dreissena polymorpha, Tapes decussatus, and two species of Venus these cells are concentrated on that particular part of the mantle which is not always covered by the shell, i.e. ”

“ The living animal buries itself in the sand with only the posterior extremity projecting into the water, so that the posterior aperture of the mantle cavity is both inhalant and exhalant.
The head is situated on the dorsal side of the body anteriorly within the anterior aperture of the mantle, from which it cannot be protruded. ”

“ I do not see: in summer the foliage is to my sight but a ragged mantle; in winter the human expression is strongest and most pathetic. Held by the feet in the grip of earth, the beaten bush strains to get away; it suggests the figure of a person crawling, or trying to crawl, the knee-like joints on the ground, the body-like trunk thrown forward, the long bare branches and terminal twigs, like the brown, thin naked arms and claw-like opened fingers of a starving scourged slave in the tropics, extended imploringly towards the land. ”

“ They live chiefly on rocks and under stones at low-water or at moderate depths; but a few forms have been discovered by the ‘Challenger’ Expedition at depths exceeding 2000 fathoms. The numerous sections of the group are principally distinguished by differences in the edges of the plates or valves which are inserted in the mantle, and in the different kinds of ornamentation upon the upper surface of the mantle-border. This, in some species, is quite smooth, in others covered with a dense mass of minute grains or scales, and in others armed with short prickly spines. ”

“ A black mantle, strewn over with golden stars, now enveloped the goddess from head to foot, leaving visible only her silvern feet, entwined by a serpent, as well as, over her head, a silvern disc, confined within the horns of a cow. ”

“ The foot, on which it glides with a slow but smooth motion over the surface of the rock on which it habitually dwells, or, if you please, on the bottom of the saucer of sea-water in which you are examining it, is a broad expansion spreading out to twice the superficies of the base of the shell. Above this is the fleshy mantle, which is so turned up as closely to invest the shell, conforming to its shape, and even fitting into the grooves between the ridges. ”

“ These two layers, therefore, when once formed cannot increase in thickness; as the mantle grows in extent its border passes beyond the formed parts of the two outer layers, and the latter are covered internally by a deposit of nacreous matter. Special deposits of the nacreous matter around foreign bodies form pearls, the foreign nucleus being usually of parasitic origin (see Pearl) .
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Let us now examine the organs which lie beneath the mantle-skirt of Anodonta, and are bathed by the current of water which circulates through it. ”

“ The two portions of the mantle touch one another along the whole line of the edge of the two valves, and, although thus in contact, may remain completely separate from one another, or [173] else become permanently united at one or more points. This fusion of the mantle edges corresponds to important changes in the organisation of the animal as a whole. The anal and branchial siphons are no more than prolongations of the mantle edges on the posterior side into a tubular form. ”

“ Coast of California (after a photograph by Fairbanks) .
Because of the tendency of mantle rock to creep down upon slopes it is generally found thicker upon the crests and at the bases of hills and thinnest upon their slopes (Fig. 164) .
In the transformation of the upper portion of the mantle rock into soil, additional chemical processes to those of weathering [156] are carried through by the agency of earthworms, bacteria, and other organisms, and by the action of humus and other acids derived from the decomposition of vegetation. ”

“ The former is much the finer species; the valves are more globose, and of a warmer colour; those that I have are even more spinous. The mantle is of a rich deep orange, with elevated ribs, corresponding to those of the valves, of a yellow hue. These ribs of the mantle are visible in aculeatum also, but in tuberculatum, they are much more strongly marked, both in form and colour. The siphons display the same orange hue as the mantle-lips, and have a finer appearance than in the other species ”

“ The body is elliptical in outline, and has fins running along each side. It is surrounded by a mantle that also incloses a cavity for the gills, which are two in number. There is a funnel-like tube opening into the mantle-cavity, and the animal can, by contracting muscles, cause the mantle-cavity to close and then throw water out through the funnel or siphon in jets. ”

“ The mantle may form a free fold on either side of the body, as in the Bivalves, or it may become largely attached to the body-wall, 2as in the Snail or the Slug, and so give rise to an air-chamber, which, when its walls are richly supplied with blood, serves as a lung. ”

“ Water from the hydrosphere is continually rising in vapor into the atmosphere, the air of the atmosphere penetrates the hydrosphere,—for its gases are dissolved in all waters,—and both air and water enter and work upon the solid earth. By their action upon the lithosphere they have produced a third envelope,—the mantle of rock waste.
This envelope also is in movement, not indeed as a whole, but particle by particle. The causes which set its particles in motion, and the different forms which the mantle comes to assume, we will now proceed to study. ”

“ We find a thin sheet of flesh lying on the shell. It is the left mantle, for there are two, one to cover the right side also, so that both together are continuous as one, and with it the animal inwraps itself.
The figure shows a portion of the right or upper lobe of the mantle. It is sometimes called the pallium, and really is the oyster's cloak, though it is always and only worn in the house. This is not true, however, of all the mollusca. The beautiful cowries, so high colored and bright, are exceptions. If you examine a common tiger ”

“ The surface is an ancient one, for the mantle of residual waste lies deep upon it, soils are reddened by long oxidation, and the rocks are rotted to a depth of scores of feet.
At present, however, the waste mantle is not forming so rapidly as it is being removed. The streams of the upland are actively engaged in its destruction. They flow swiftly in narrow, rock- walled valleys over rocky beds. ”

“ Most of the relics of life found in the stratified rocks belonged to animals or plants which lived in salt water. Because of their structure, their composition, their distinctive markings, and the remains of life which they contain, it is confidently inferred that most of the stratified rocks which lie beneath the mantle rock of the land were originally laid down in beds beneath the sea, and that the familiar processes of the present time furnish the key to their history. ”

“ It was found after many trials that a blend of these earths in certain proportions gives a mantle that yields a pure white light, while any preponderance of one or another would impart some tint to the light. ”

“ Free-swimming pelagic forms which may be either simple or compound, and the adult of which is never provided with a tail or a notochord. The test is permanent and may be either well developed or very slight. The musculature of the mantle is in the form of more or less complete circular bands, by the contraction of which locomotion is effected. The branchial sac has either two large or many small apertures, leading to a single peribranchial cavity, into which the amis opens. Alternation of generations occurs in the lifehistory, and may be complicated by polymorphism. ”

“ As a result there is everywhere forming a mantle of rock waste which covers the land. It is well to imagine how the country would appear were this mantle with its soil and vegetation all scraped away or had it never been formed. The surface of the land would then be everywhere of bare rock as unbroken as a quarry floor. ”

“ By the secretive action of its mantle it gathers from the water in which it lives, material to build a shell with a rough and rugged exterior for its enemies, and adapted to resist the chemical activities by which it is surrounded, and a perfectly smooth lining suitable as an interposition for its own delicate organism. ”

“ A partly draped female figure is seated upon a rock, her head turned away and resting upon her left hand, the left elbow being supported upon her right thigh. A black mantle is draped across one knee, and contrasts strongly with the flesh and a white garment which is spread upon the rock. In the background is suggested a tree trunk and a mass of foliage, and the figure is in strong effect of light from the upper right. ”

“ THE THICKNESS OF THE MANTLE. In any locality the thickness of the mantle of rock waste depends as much on the rate at which it is constantly being removed as on the rate at which it is forming. On the face of cliffs it is absent, for here waste is removed as fast as it is made. Where waste is carried away more slowly than it is produced, it accumulates in time to great depth. ”

“ Earthy matter is being continually transferred from land to sea, and chiefly from high land. Rarely does it start from any point distant from the shore and move uninterruptedly to it. It is transported a short distance and lodged, to be again picked up, carried forward another step in its journey, and lodged again. For a very large part of the earth’s surface it would be true to say that its mantle rock is material in transit from higher land to the sea. ”

“ The shell-gland is formed on the dorsal surface, and the mantle arises as two lateral lobes which afterwards unite by their ventral edges to form the tubular mantle of the adult. The anus is not formed till a very late period of the development. The foot arises as a prominence on the ventral surface and grows forward, and at the end of five or six days the velum atrophies and the foot becomes the organ of locomotion ”

“ As the icy mantle gradually melted off the face of the earth these plants would occupy the newly exposed soil, and would thus necessarily travel in two directions, back towards the arctic circle and up towards the alpine peaks. The facts are thus exactly explained by a cause which independent evidence has proved to be a real one, and every such explanation is an additional proof of the reality of the cause. ”

“ Trees overthrown by the wind, roots and all, turn over the soil and subsoil and mingle them together. Bacteria also work in the waste and contribute to its enrichment. The animals living in the mantle do much in other ways toward the making of soil. They bring the coarser fragments from beneath to the surface, where the waste weathers more rapidly. Their burrows allow air and water to penetrate the waste more freely and to affect it to greater depths.
ANTS. In the tropics the mantle of waste is worked over chiefly by ants. ”

“ Unlike the animals which we have been considering, these mollusks have no siphons and the shell is open all the way around save at the hinge, and the edge of the mantle is provided with little, round, black eyes. It is an interesting sight to observe a beach at low water, the receding tide having left on the shore or in little pools of water hundreds of these mollusks, attached by a byssus to bits of sea weed. ”

“ In many regions the metamorphic and granite rocks would be found much more widely extended than they appear to be, if all the sedimentary beds were removed which rest unconformably on them, and which could not have formed part of the original mantle under which they were crystallised. Hence, it is probable that in some parts of the world whole formations have been completely denuded, with not a wreck left behind. ”