Spicule

“ These also must be looked upon as the simple result of chemical deposition, the form of the deposit being somewhat modified in conformity with the surrounding tissues, just as in the simple experiment the form of the concretionary precipitate is affected by the heterogeneity, visible or invisible, of the matrix. Lastly, the simple needles of amorphous silica, which constitute one of the commonest types of spicule, call for little in the way of explanation ”

“ In Plakina the spicules are all of about the same size, neither very large nor very small, but in higher forms we usually find some of the spicules enlarged to form megascleres and others reduced to form microscleres. The megascleres play the principal part in building up the skeleton while the microscleres are usually scattered through the mesogloea.
Triaene Series of Megascleres.—When three rays (cladi) of the tetract resemble one another, while the fourth (shaft) differs in some respect the spicule is termed a triaene. ”

“ Flesh-spicules very numerous in the parenchyma and especially the external membrane, as a rule considerably more slender and more sharply pointed than the gemmule-spicules, covered with straight spines which are often longer at the middle of the shaft than at the ends. ”

“ Again, it is not necessarily at variance with our hypothesis to find that, in the adult sponge, the larger spicules may greatly outgrow the bounds not only of actual cells but also of the ciliated chambers, and may even appear to project freely from the surface of the sponge. For we have already seen that the spicule is capable of growing, without marked change of form, by further deposition, or cry­stal­li­sa­tion, of layer upon layer of calcareous molecules, even in an artificial solution ”

“ Skeleton-spicules smooth, sharply pointed, nearly straight, moderately slender, about twenty times as long as their greatest transverse diameter. Flesh-spicules occasionally amphioxous or birotulate and with a single shaft, more frequently consisting of many shafts meeting in a distinct central nodule, which is itself smooth; the shafts irregularly spiny, usually more or less nodular at the tip, which often bears a distinct circle of recurved spines that give it a rotulate appearance. ”

“ In the more delicate species, as that of Venus’ flowerbasket, the cells are formed by a trellis work of large spicules of silica. Groups of cells congregate in the ground substance and secrete a network of cylindrical fibres and spicules, which, although they remain to a certain extent separate, are always beautifully adapted for purposes of support. ”

“ There are many other forms of spicules to reward the painstaking microscopist who searches for them, some of them minute and requiring the higher powers of the instrument and careful examination of the lighter washings, but the most beautiful and distinctive are those which we have seen and which can be easily demonstrated with the most ordinary microscope. ”

“ But if such a physical explanation of the forms of our spicules is to be accepted, we must seek at once for some physical agency by which we may explain the presence of the solid material just at the junctions or interfaces of the cells, and for the forces by which it is confined to, and moulded to the form of, these intercellular or interfacial contacts. It is to Dreyer that we chiefly owe the physical or mechanical theory of spicular conformation which I have just described,—a theory which ultimately rests on the form assumed, under surface-tension, by an aggregation of cells or vesicles. ”

“ Through these tubes water laden with food enters the gastric cavity, where the food is digested, the water and undigested particles passing out through the osculum. Crush a bit of dried sponge, or boil a bit of soft sponge in caustic potash and mount on a glass slide. Examine under a microscope and note the abundance of spicules and the variety in their form. Two kinds may always be found, and [Pg 86] sometimes three. These spicules are composed of carbonate of lime and can be dissolved by pouring on to them a drop of hydrochloric acid. ”

“ Spicula of three different kinds; simple needles, radiate and geminate mixed. The simple needles thin spindle-shaped, often curved. The radiate spicula commonly with three or four, rarely five or six, curved rays. The geminate-radiate spicula commonly with three or four, rarely two or five, shanks on each end, often different on the two ends of the middle rod. Number and form very variable. All or most of the shanks more or less bent and thorny.
Dimensions.—Diameter of the capsule 0.1 to 0.3, length of the spicula 0.05 to 0.2. ”

“ The only character sufficient for the constitution of genera in this transformistic group is found in the form and composition of the spicula; the very variable form of the jelly-calymma and the enclosed central capsule being without value for this purpose. But also the form of the spicula is very variable, and not always constant. In some species the particular form of the spicula is transmitted by constant heredity, whilst in others it is very inconstant, even in one and the same individual. ”

“ The spicula are scattered throughout the alveolate calymma. Fig. 2. Thalassoplancta brevispicula, n. sp. (vel Lampoxanthium brevispiculum) , × 120 36 The central capsule contains numerous clear vacuoles, and in the cortical zone a layer of large oil-globules. The central nucleus includes numerous dark nucleoli. The calymma is alveolate. The spicula lie only in the cortical zone. Fig. 3. Thalassoxanthium cervicorne, n. sp., × 300 33 The central capsule is filled up by clear vacuoles and contains a large central nucleus, with a single nucleolus. The spicula surround the thin calymma. ”

“ Fig. 3. Sphærozoum alveolatum, n. sp., × 400 43 A single central capsule, filled up by crystal-spores. Numerous geminato-radiate spicula and spherical xanthellæ lie between the capsule and the including thick-walled alveole. In the jelly-calymma, between the capsule and the alveole, numerous thin ramified pseudopodia are expanded. Fig. 4. Sphærozoum geminatum, n. sp., × 400 45 A single central capsule, with a central oil-globule, surrounded by numerous spicula and spherical xanthellæ. The jelly-substance of the calymma is expanded between the points of the spicula. Fig. 5. ”

“ The surface is compact and smooth, of a delicate purplish-grey hue, with a few minute orifices, each surrounded by a small paler area.
The spicula in this noble species are various: simple rods, straight, thick, long, slightly spindle-shaped, blunt at both ends, with a linear axis; three-rayed, large, stout, very unequal angled, without any central channel; a number of very small five- and six-rayed stars, the rays projecting in different planes. They are set in a dense, yellow, gelatinous flesh, in which we may at all times discover many gemmules, or eggs ”

“ Microscopic Structure—The pericarp consists of two layers, the outer being composed of yellow thick-walled cells. The inner layer is twice as broad and exhibits a soft shrunken parenchyme, traversed by thin fibro-vascular bundles. The cells of the outer layer especially are the seat of the fine granular colouring matter. If it is removed by an alcoholic solution of potash, a cell-nucleus and drops of fat oil make their appearance. ”

“ A phenomenon similar to one we have already seen in cell-division among plants now shows itself. The nucleus becomes broken up into a number of filaments, which lie together in a bundle, each filament stretching from pole to pole of the spindle. Exactly in its central point every filament shows a knot-like enlargement, and from the close approximation of the knots there results a thick zone of protoplasm in the equator of the spindle. ”

“ Here we have only the spike to consider, as the funnels are the same as in germanium, and the central globe is that of titanium, omitting the eight atomed centre. The cone of the spike we have had in silver (see p. 729, May) , and it is set free on the proto level. The spike, as in zinc, becomes a large sphere, with the single septet in the centre, the remaining six bodies circling round it on differing planes. They break up as shown. ”

“ Projectiles excite a motion in fluids as they pass through them, and this motion arises from the excess of the pressure of the fluid at the fore parts of the projectile above the pressure of the same at the hinder parts; and cannot be less in mediums infinitely fluid than it is in air, water, and quicksilver, in proportion to the density of matter in each. ”

“ Dermal Bones of Reptiles. Tilgate Forest.
The structure of these bodies is very remarkable; upon closely inspecting the under side, and the surface exposed by a transverse fracture, very minute osseous spicula, decussating each other at right angles, are distinctly seen; as shown in Lign. 208, fig. 1a. In fig. 1b, a thin slice of the same, highly magnified, and viewed by transmitted light, displays medullary canals, with very fine lines radiating from them. The peculiar character of this organization consists in the disposition of the straight bony spicula ”

“ The capsules or thécæ (θἡκη, a case) , a magnified group of which is represented in fig. 11, consist each of an aggregation of cells, fixed to a stalk (fig. 12) ; and along the back of the capsule is a close row of thicker cells, forming an elastic ring, the an ́nulus. When the seed-like bodies or spores (σπορἁ, a seed) are ripe, the annulus becomes straightened from its elastic power, and tears the capsule open, so that the spores are set free and scattered. ”

“ The case of the spherical nucleus is closely akin to the spherical form of the yolk within the bird’s egg222. But if the substance of the cell acquire a greater solidity, as for instance in a muscle {166} cell, or by reason of mucous accumulations in an epithelium cell, then the laws of fluid pressure no longer apply, the external pressure on the nucleus tends to become unsymmetrical, and its shape is modified accordingly. “Amoeboid” movements may be set up in the nucleus by anything which disturbs the symmetry of its own surface-tension. ”

“ FIG. 3.
Until reaching the point A we suppose that the particle does not feel appreciably the repulsion of the surface. After A the repulsion bends the path of the particle round until B is reached, and after B the repulsion becomes inappreciable again. The effect is the same as a perfectly elastic ball bouncing on a perfectly smooth surface, and consequently the angle to the surface at which the corpuscle comes up is equal to the angle at which it departs. ”

“ Each of these little particles, no matter how quiet the air as a whole may seem, is in a state of intensely rapid movement. Picture to yourself incalculable myriads of little objects, each dashing about with a speed as great as that of a rifle bullet, and often indeed far greater. The little particles are so minute that it would take about fifty millions of them, placed side by side, to extend over a single inch. The smallest object which we can discern with a microscope is perhaps one hundred-thousandth of an inch in length. ”

“ Upon the first Sight I could discover nothing but a Parcel of small Salts nimbly floating in the Liquor, but in a very short time the Appearance was changed, and these saline Particles were now shot out as it were into Crystals of an incredible Tenuity and Sharpness, with something like Knots here and there, from which they seemed to proceed, so that the whole Texture did in a manner represent a Spider’s Webb, tho’ infinitely Finer, and more Minute; and yet withal so rigid were these pellucid Spicula, or Darts, that they remained unaltered upon my Glass for several Months (13) . ”

“ Spikelets 1-flowered, crowded in a dense spike or spike-like panicle. Lower glumes persistent, membranaceous, acute, ciliate-carinate, awnless; flowering glume similar, a little longer, and a little exceeding the palet. Stamens 3.—Low cespitose annuals; spike often scarcely exserted from the upper sheath. (Name from ἕλος, a meadow, and χλόα, grass.)
H. schœnoìdes, Host. Usually nearly prostrate and tufted; leaves rather rigid, tapering to a sharp point; spike oblong, thick, 7–20 ́ ́ long. ”

“ The main mass of the jelly-colony is filled up by large alveoles; the entire surface is densely covered with spicula, and beyond this skeleton-cover lie the spherical central capsules, each with an oil-globule. ”

“ The perfect transparency of the body when silicified, and the rich tints it has acquired from metallic solutions, and the compressed state in which it is often found, seem to indicate that the original mass was a soft gelatinous substance, like that of the Actinia, strengthened by spicula; for numerous tri-radiate spines, like those on the left-hand of fig. 5, Lign. 75, occur occasionally in chalk specimens. ”

“ The fibres easily break across at the joints; and the last few segments are often narrowed and rounded, so as to form a blunt point. When they have been left in water, they exhibit colourless tubular sheaths surrounding and extending beyond them. These sheaths consist of the consolidated outer portions of the cell-walls; for when the cells undergo transverse division, and expand by growth in the direction of the length of the filament, the original septa or inner walls are broken through, and their remains may often be seen on the inner surface of the sheath, appearing as little teeth. ”

“ The hairs are attached to the sides of the stamens, towards the lower part or base. The stamens should be carefully picked off with forceps, and placed on a slide in a drop of water; the hairs should then be separated with the mounted needles, and a cover applied. Under a low power, the hairs are seen to be beaded or monil ́iform (moníle, a necklace) , and of a fine purple colour (Pl. I. fig. 22) .{33} On applying a high power, as the 1⁄4-inch, the individual cells will come distinctly into view, and the nucleus will be seen very clearly as a roundish granular mass (Pl. I. fig. 23 a) . ”