Ectoplasm

“ But attentive observation will demonstrate very definitely that the ectoplasm here is stationary to the same degree as in proteus.{79} The stationary properties of the ectoplasm are however not properly a matter for discussion; for five minutes’ observation of a proteus, discoides, annulata, particularly a laureata, under 300 diameters magnification, will convince anyone that the ectoplasm is stationary while the surface film, with attached particles, moves over it. No one can possibly come to any other conclusion. ”

“ The motive power is supposed to have its source in the contractility of the ectoplasm. The endoplasm is held to be a passive stream, not an active stream as Ewart supposed to be the case in plant cells. The power of contractility is held to be due to the process of gelation of endoplasm into ectoplasm, which is due to a change of phase, the fluid part of the endoplasm becoming dispersed and thereby developing surface energy in proportion as the amount{86} of surface of the fluid is increased. This increase of surface produces the phenomenon of contractility. ”

“ A Radiolarian "central-capsule" (p. 75) with its endoplasm and nucleus may regenerate its ectoplasm, but the isolated ectoplasm being non-nucleate is doomed. A "central capsule" of one species introduced into the ectoplasm of another, closely allied, did well. All non-nucleate pieces may exhibit characteristic movements, but appear unable to digest; and they survive only a short time. ”

“ It is not possible to define exactly what occurs in the case of the ectoplasm, nor, on account of its vital connection with the medium and its evanescent nature, has it been separated and subjected to even the roughest chemical analysis which might show whether it is composed of those earthly elements with which we are familiar. Is it rather some coagulation of ether which introduces an absolutely new substance into our world? ”

“ On account of the relatively large size which the contractile vacuole attains it bulges inwards beyond the limits of the ectoplasm and comes to lie chiefly in the endoplasm, to which it is sometimes, but erroneously, ascribed. In the most highly differentiated Protozoa, for instance, the Ciliata, the ectoplasm contains an apparatus of excretory channels, situated in its deeper layers, and forming as it were a drainage-system, from which the contractile vacuoles are fed. ”

“ A sound man and a brilliant one, hard to corrupt or fool. It makes ectoplasm sound organic, does it not?"
I nodded agreement, and my head felt heavy, as if full of sober and important matters. "As for me," I went on, "I never have had much chance to examine the stuff. Whenever I get hold of an ectoplasmic hand, it melts like butter."
"They generally do," the judge commented, "or so the reports say. Yet they themselves are firm and strong when they touch or seize." ”

“ This layer is designated the ectoplasm, as distinguished from the remainder of the cell contents, the endoplasm. When bacteria are suddenly transferred from a given medium into one of decidedly greater density, there sometimes results a contraction of the endoplasm, due to the rapid diffusion of water. ”

“ The most marked property of this ectoplasm, very fully illustrated in the photographs, is that it sets or curdles into the shapes of human members—of fingers, of hands, of faces, which are at first quite sketchy and rudimentary, but rapidly coalesce and develop until they are undistinguishable from those of living beings. ”

“ The ectoplasm is the protective layer of the body, and is also the portion most concerned in movement, in excretion, and perhaps also in sensation and in functions similar to those performed by the nervous systems of higher animals. ”

“ Léger thinks only the deutomerite becomes thus segmented, the protomerite remaining small and undivided. The nucleus remains single, so that there is no question as to the unicellular or individual nature of the entire animal.
The general cytoplasm usually consists of distinct ectoplasm and endoplasm, and is limited by a membrane or cuticle (epicyte) , secreted by the former. The cuticle varies considerably in thickness, being well developed in active, intestinal forms, but very thin and delicate in non-motile coelomic Minute structure. forms (e.g. Diplodina) . ”

“ The two most striking parts of the protoplast are the cytoplasm and the nucleus. The part of the protoplast lining the innermost part of the wall is the ectoplast, which is less granular and slightly denser than most of the cytoplasm. The cytoplasm is decidedly granular in structure.
In the cytoplasm occurs one or more cavities, vacuoles, filled with cell sap. Embedded in the cytoplasm are numerous chromatophores, which vary in color in the different cells, from colorless to yellow, to red, and to green. The nucleus is the seat of the vital activity of the cell, and the seat of heredity. ”

“ Unlike the fat-body, however, they arise in embryonic life from the ectoderm, either by delamination or by immigration, just behind the tracheal involutions.
The separate cells of each cluster are usually separate, but in rare cases may fuse in pairs or form smaller clusters. In shape they are round or oval, often sending out pseudopodia-like processes, by which they are attached to the tracheal twigs or to each other. “The cytoplasm, which is very abundant, is full of yellowish granules and is sometimes radially situated towards its periphery. ”

“ It is very unusual for all the layers to be established at the same time. As a general rule the ectoderm and endoderm, which may be called the primary layers, come first, and later the mesoderm is developed from one or other of them. There are two main methods in which the first two are differentiated—invagination and delamination. The former is generally found in small eggs, in which the embryo at the close of cleavage assumes the form of a sphere, having a fluid or gelatinous material in its centre, and bounded externally by a thin layer of protoplasm, in which all the nuclei are contained. ”

“ In some cases the protoplasm at the circumference is so modified as to give the appearance of a limiting membrane called the cell wall. In brief, then, a cell is a mass of nucleated protoplasm; the nucleus may have a nucleolus, and the cell may be limited by a cell wall. Every tissue of the human body is formed through the agency of protoplasmic cells, although in most cases the changes they undergo are so great that little evidence remains of their existence. ”

“ The former, for instance, contains a rounded nucleolus or “germinal spot,” certain conspicuous granules or strands of the peculiar substance called chromatin, and a coarse meshwork of a protoplasmic material known as “linin” or achromatin; the outer protoplasm, or cytoplasm, is generally believed to consist throughout of a sponge-work, or rather alveolar meshwork, of more and less fluid substances; and lastly, there are generally to be detected one or more very minute bodies, usually in the cytoplasm, sometimes within the nucleus, known as the centrosome or centrosomes. ”

“ The ecto sarc may be differentiated into a specially modified cortical layer, and well-marked muscular fibres may be developed. Morever, the endoplast, or " nucleus," becomes an organ of reproduction, the germs of the young being given off by division from it. Very generally, a small body the so-called " nucleolus," but which has, admittedly, nothing to do with the structure so named in a true cell, and may be termed the " endoplastula " is to be found close to the nucleus, and there is some ground for supposing it to be a testis. ”

“ It presents two surfaces, which are respectively outer and inner, and is formed of a layer of somewhat thickened germinal epithelium separated by a basement membrane from a central core of stroma. The epithelium is far thicker on the outer surface than on the inner, and the primitive ova are entirely confined to the former. The cells of the germinal epithelium are irregularly scattered around the primitive ova, and have not the definite arrangement usually characteristic of epithelial cells. Each of them has a large nucleus, with a deeply staining small nucleolus, and a very scanty protoplasm. ”

“ Chordata. In the Vertebrata, the primitive generative cells (often known as primitive ova) are early distinguishable, being imbedded amongst the cells of two linear streaks of peritoneal epithelium, placed on the dorsal side of the body cavity, one on each side of the mesentery (figs. 405 C and 410, po) . They appear to be derived from the epithelial cells amongst which they lie; and are characterized by containing a large granular nucleus, surrounded by a considerable body of protoplasm. The peritoneal epithelium in which they are placed is known as the germinal epithelium. ”

“ The reproductive organs or gonads are borne on the mesenteries, the germinal cells being derived from the inner layer or endoderm.
In common with all Coelenterate animals, the walls of the columnar body and also the tentacles and peristome of Actinia are composed of three layers of tissue. The external layer, or ectoderm, is made up of cells, and contains also muscular and nervous elements. The preponderating elements of the ectodermic layer are elongated columnar cells, each containing a nucleus, and bearing cilia at their free extremities. ”

“ More complete differentiation of the protoplasmic substance into endosarc and ectosarc, the former being a slightly viscous granular liquid, and the latter approaching the tenacity of a membrane: a nucleus and contractile vesicle; pseudopodia few and large, being in reality lobose extensions of the body which neither ramify nor coalesce, having well-defined margins, and not exhibiting any movement of granules on their surface, the circulation in their interior being entirely dependent on the changes of form which the body undergoes as a whole. ”

“ The cell-contained protoplasts thus variously changed are fused together into tissues in which their individualities are practically lost; but they nevertheless remain connected throughout by permeable strands of protoplasm. Arising by complication of the outer and inner layers of the embryo and growing more unlike as their units become more obscured, these tissues are formed into systems, which develop into sets of organs. Some of the resulting structures are localized and special but others are everywhere interfused. ”

“ Indeed the segregation and isolation of different protoplasmic substances in different cleavage cells occurs during the cleavage of the egg in all animals, though such differentiations are much more marked in some cases than in others.
Fig. 31. Gastrula and Larva of Styela, showing the cell lineage of various organs, and the distribution of the different kinds of protoplasm to these organs. Muscle cells are shaded by vertical lines, mesenchyme by horizontal lines, nervous system and chorda by stiples. ”

“ From one part of the periphery of the ectoderm proliferation of cells takes place and gives rise to a layer of scattered nuclei over the whole surface of the yolk. The region of proliferation marks the anal side of the ectoderm, and the layer of nuclei forms the perivitelline membrane. This process must be regarded as equivalent to the first stage of invagination, the yolk being surrounded by hypoblast cells or their nuclei. Later on the same anal edge of the ectoderm forms another cellular layer, the endoderm proper, which forms a continuous sheet below the ectoderm. ”

“ The plates forming the corona are, like all the elements of the skeleton of Echinodermata, products of the connective tissue which underlies the ectoderm, which in Echinoidea remains in a fully developed condition covering the plates, and does not, as in Ophiuroidea, dry up so as to form a mere cuticle. The ectoderm consists of the same elements as that of Asteroidea, viz. delicate tapering sense-cells with short sense-hairs, somewhat stouter supporting cells and glandular cells. ”

“ In the section under discussion the ectoderm (ec) is a very thin membrane on top of a considerable mass of yolk, while no entoderm can be distinguished. The amnion (a) completely surrounds [259] the embryo as an irregular membrane of some thickness in which no arrangement into layers can be seen. The epidermal ectoderm (ep) is composed of the usual loosely arranged cells, so that it is clearly distinguishable from the compactly arranged cells of the nervous layer (nl) , from which it is separated by only a line. ”

“ Finally, as so many and such widely different causes excite aggregation, it would appear that the living matter within the gland-cells is in so unstable a condition that almost any disturbance suffices to change its molecular nature, as in the case of certain chemical compounds. And this change in the glands, whether excited directly, or indirectly by a stimulus received from other glands, is transmitted from cell to cell, causing granules of protoplasm either to be actually generated in the previously limpid fluid or to coalesce and thus to become visible. ”

“ The outer grey part of the body, which is attached at or near its The Test. posterior end and penetrated by the two apertures, is the “test.” This is a firm gelatinous cuticular secretion upon the outer surface of the ectoderm, which is a layer of flat cells. Although at first produced as a cuticle, the test soon becomes organized by the migration into it of cells derived from the mesoderm. A. Kowalevsky has shown that cells of the mesenchyme of the larva make their way through the ectoderm to the exterior during the metamorphosis, and become the first cells of the young test. ”