Shell heap

“ To creatures that sometimes floated, a thick and heavy shell would have been inapplicable; and as a thin shell, inclosing air, would be exposed to various, and often intense degrees of pressure at the bottom, we find a series of provisions to afford resistance to such pressure, in the mechanical construction both of the external shell, and of the internal transverse plates which formed the air-chambers. ”

“ If the hollow spheroidal shell were strong enough to sustain, as a spheric dome, the tangential thrust of its own weight and the attraction of the nucleus, the shell would be left behind altogether by the nucleus, and the latter might be conceived as an independent globe revolving, centrally or excentrically, within a shell outside of it. ”

“ It is very common to find shells unnaturally flattened, or compressed in various ways and degrees, often without any fracture in the shell or cast; a circumstance which certainly could never happen to the shell, unless it was in a plastic state, or in a state of partial solution.
16. A specimen of carbonate of lime, on its surface a mass of sub-parallel tubes, connected by short lateral processes. ”

“ Chambered nautilus is brother to the octopus, but he wears his castle permanently—and on the outside.
THE SHELL AS AN ARCHITECT. . .HOW DOES HE DO IT? Picture a vast undersea factory with billions of shells in constant production. Each is made slowly and entirely of lime which the little animal inside extracts from its food, almost from the first day of its life. Each shell builder flawlessly follows the shape and design of the species to which it belongs. ”

“ Some of the shells are so deeply corroded, that no portion of the original surface is preserved, excepting the lowermost bead-like scales; and the whole shell has so rugged an aspect, that the successive whorls of the worn-down valves might easily be overlooked. ”

“ That others of these Shells, according to the nature of the substances adjacent to them, have, by a long continuance in that posture, been petrify'd and turn'd into the nature of stone, just as I even now observ'd several sorts of Wood to be. That oftentimes the Shell may be found with one kind of substance within, and quite another without; having, perhaps, been fill'd in one place, and afterwards translated to another, which I have very frequently observ'd in Cockle, Muscle, Periwincle, and other shells, which I have found by the Sea side. ”

“ One of the largest of their shells bursted within nine or ten yards of me: there was a single rock close by, about the size of a butt; and I got instant shelter under it in time to avoid the fury of the shell. Where it burst the earth was torn in such a manner that two or three butts might easily have gone into the hole it made, and it threw great quantities of stones and dirt to a considerable distance. ”

“ As the shell, when attached to the living animal, was probably a quarter of an ounce heavier than these dry dead shells, and the specific gravity of the body of the animal may have exceeded that of water to the amount of another quarter of an ounce, there remains about half an ounce, for the weight of fluid which being introduced into the siphuncle, would cause the shell to sink; and this quantity seems well proportioned to the capacity both of the pericardium, and of the distended siphuncle. ”

“ It is in accordance with certain variations in the shape and disposition of this mantle and collar, that shells assume such very different shapes. Sometimes the whorls or spiral ridges, are projected or thrown far out, and this produces the turbinated shell. Sometimes they scarcely rise above each other, but rather spread towards the sides, and then we have the discoid shape. Generally speaking, the whorls of a shell take a direction from left to right, but occasionally an opposite one ”

“ If we imagine a delicate discoid spiral shell of elegant form, marked with curved and diverging grooves, and inhabited by a tiny piece of clear jelly without organs, but capable of projecting the substance of its body (called “sarcode”) in the finest possible filaments through perforations in the surface of its shell, this first principal representative of the deep sea soundings is before us. In our prepared and mounted specimen it is the shell alone which we see; the delicate tenant has of course long since perished, and its beautiful envelope alone is left ”

“ The extreme brittleness of the shell is such, that, although common, it is very rarely seen so perfect as here represented, from shells in my own cabinet. All the figures I have seen are very defective. ”

“ 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. ”

“ The outer shelly portion of this body consists of horny layers, alternating with calcified layers, in which last may be seen a hexagonal arrangement. The soft, friable substance, that occupies the hollow of this boat-shaped shell, is formed of a number of delicate plates, running across it from one side to the other in parallel directions, but separated by intervals several times wider than the thickness of the plates; and these intervals [Pg 238] are in great part filled up by what appear to be fibres, or slender pillars, passing from one plate or floor to another. ”

“ Each tube secretes a tiny amount of lime which instantly adheres to the shell. The animal builds his shell to the proper size and thickness and determines its ridges and whorls. Some kinds of shells take two to five years to reach maturity. Others keep growing all their lives. Color tubes are spaced like holes on a player piano roll allowing pigments to tint the shell at the right spots in the growing design. ”

“ The peculiar structure of the sheath, which is the strongest part of the shell, namely, its division into oblique layers, separable by a slight force, doubtless is subservient to the repeated breakage of the summit. In some species of Tetraclita and of Balanus, gradual disintegration of the upper part of the shell is a necessary element in the growth of the animal, in order that the orifice may increase in size, and here we have mechanical breakage equally necessary. ”

“ The buoyancy of the shell seems exactly adapted to the weight of the animal; and this proportion is kept up by the addition of new air-chambers as the body increases in size. In the modern seas this singular little group stands entirely isolated, and its individuals are so rare that it is difficult to procure perfect specimens for collections, though its mechanical structure and advantages for the struggle for existence seem of the highest order. ”

“ Respecting the construction of the shell it may be observed that it is produced in the thickness of the mantle, or cloak-like covering which envelopes the body of the animal; the formation commences at the small end or spire, and gradually goes on, whorl upon whorl, as the still widening circles which give the ridgy appearance to most univalves, are called. ”

“ Afterwards I view’d it every way with a better Microscope and found it on both sides, and edge-ways, to resemble the Shell of a small Water-Snail with a flat spiral Shell: it had twelve wreathings, a, b, c, d, e, &c. all very proportionably growing one less than another toward the middle or center of the Shell, where there was a very small round white spot. I could not certainly discover whether the Shell were hollow or not, but it seem’d fill’d with somewhat, and ’tis probable that it might be petrify’d as other larger Shels often are, such as are mention’d in the seventeenth Observation. ”

“ Although shells take on many different shapes, they are much alike inside. Each has a foot, a breathing siphon, a tiny brain and heart, and a fleshy mantle which secretes lime for shell-building. Most true mollusks have eyes, but a few are blind. ”

“ The shell becomes like a boat it is true, but its inhabitant neither points a sail nor plies the oar, but propels itself along stem foremost by a muscular action, which by alternately compressing and loosening a kind of siphon, throws out jets or gushes of water, which by the resistance they meet with from the surrounding fluid, give the desired onward motion, and away the swimmer goes, his long arms gathered closely together, and streaming behind like the tail of a comet, and its round eyes keeping a sharp look-out on either side. ”

“ The surface of any shell, whether discoid or turbinate, may be imagined to be generated by the revolution about a fixed axis of a closed curve, which, remaining always geometrically similar to itself, increases continually its dimensions: and, since the rate of growth of the generating curve and its velocity of rotation follow the same law, the curve traced in space by cor­re­spon­ding points {554} in the generating curve is, in all cases, a logarithmic spiral. In discoid shells, the generating figure revolves in a plane perpendicular to the axis, as in Nautilus, the Argonaut and the Ammonite. ”

“ Secondly, besides this general arch-like form, the shell is further strengthened by the insertion of ribs, or transverse arches which give to many of the species their most characteristic feature, and produce in all, that peculiar beauty which invariably accompanies the symmetrical repetition of a series of spiral curves. (See Pl. 37, Fig. 1—-10.)
From the disposition of these ribs over the surface of the external shell, there arise mechanical advantages for increasing its strength, founded on a principle that is practically applied in works of human art. ”

“ The cause of their sinking, therefore, is not death of the creatures, but weight of their shells. The thickening consists in a deposit of calcareous matter upon the outside of the proper wall after the creatures' full growth, which not only increases the weight, but alters the contour of the shell. ”

“ The original movement of the parts towards their common centre, would naturally form a whirl there, which would continue in the turning of the new formed globe upon its axis, and the greatest diameter of the shell would be in its equator. If by any accident afterwards, the axis should be changed,” [viz. by the impinging of a Buffon’s comet’s tail or the delivery of a Darwin’s moon] “the dense internal fluid by altering its form must burst the shell and throw all its substance into the confusion in which we find it!” There’s an air gun for your worships! ”

“ The transitions of these shells, it must be confessed are so various as to render it extremely difficult, if not unsafe, to determine where one species ends and another commences, the difference in the colours affords no sufficient data, neither is the form of the shell, nor the height of the spire so uniformly certain as to constitute a precise criterion. ”

“ Shell, when full grown and mature, is solid, oval, convex, very smooth, involute; the spire entirely posterior, very small, often concealed by a calcareous layer deposited by the lobes of the mantle, leaving in some species a small cavity like an umbilicus; aperture longitudinal, very narrow, slightly curved, as long as the shell, with edges internally dentated, and notched at each extremity. ”

“ On the other hand, shells occurring in sheltered situations, estuaries, narrow straits, or even on open coasts where there is plenty of shelter from the waves, are comparatively of great size, with a well-developed, sometimes produced spire, and a mouth small in proportion to the area of shell surface. ”

“ This membrane or mantle sometimes extends some distance beyond the edge of the shell, and, being of a light and filmy appearance, may have been mistaken for a sail hoisted by the creature to catch the breeze, while its long arms, thrust up into the air or down into the water, may have been thought to be masts or oars, so that the poets are not so much to be blamed, if they say as Wordsworth does. ”

“ We may always know the different species by the forms and patterns of the shells in which they live. Some have very regular shells and prettily marked. These are usually rounded or arched on one side and flat on the other.
When you are looking for various microscopic objects in pond water you will often see these tiny shells [90] among the sediment on your slides, and if you will patiently wait a few moments you will soon see delicate, transparent arms slowly pushing out on every side like cautious feelers. (Figure 2, Amœba in Shell.—Carpenter, p. 445.) ”

“ The first is called into play by the property peculiar to the hinge system that unites the double shell, of gaping wide open, in consequence of which extraneous substances rush in with the current of water, such as minute fragments of quartz, molecules of plants, &c., which, being detained either circling in the cavity, or eddying round the hinges, are seized on in the course of their revolutions, and entangled in the parenchyma of the various organs, which is specially secreted from the mantle, till it becomes enveloped by layers of solid shell. ”

“ Everyone who has spent a little time in naturalising on the shore, has noticed how often you may find univalve shells, such as those of the whelk and periwinkle, with the top of the shell knocked off. This is nearly always the case with the dead shells that you find strewn along the tide-line; and after a storm, on a rocky coast, you may find shells that still contain the living tenant, in the same sad condition. And you may also meet not infrequently with shells, dead or living, that bear evidence of the owners' efforts to repair them after an accident to the spire. ”