Germinal vesicle

“ He found in the impregnated, but not yet segmented, germinal disc a cavity which, as he suggests, might well have been occupied by the germinal vesicle. It is not unreasonable to suppose that the membrane, being composed of formed matter and able only to take a passive share in vital functions, could, without thereby influencing the constitution of the ovum, be ejected. ”

“ In Figure 1.138 the tufted it prochorion (dd apostrophe) encloses the germinal vesicle, the wall of which consists of the two primary layers. Between the outer (a) and inner (i) layer the middle layer (m) has been developed in the region of the germinative area. In Figure 1.139 the embryo (e) begins to separate from the embryonic vesicle (ds) , while the wall of the amnion-fold rises about it (in front as head-sheath, ks, behind as tail-sheath, ss) . ”

“ Fig. 1.—Unripe ovum of Toxopneustes lividus (copied from Hertwig) .
Every ovum as it approaches maturity is found to be composed (Fig. 1) of (1) a protoplasmic body or vitellus usually containing yolk-spherules in suspension; (2) of a germinal vesicle or nucleus, [Pg 522] containing (3) one or more germinal spots or nucleoli. It is with the germinal vesicle and its contents that we are especially concerned. This body at its full development has a more or less spherical shape, and is enveloped by a distinct membrane. ”

“ The coalescence of the two nuclei within the substance of the germinal vesicle causes the latter to secrete a wall, and to form a new plant by division, being nourished the while by the mother plant, from whose tissues the young embryo plant contained in the seed only becomes free when it is in an advanced stage of differentiation. ”

“ Before Schwann had published his classical memoir in 1839, von Baer and other observers had recognized within the animal ovum the germinal vesicle, which obviously bore to the ovum the relation of a nucleus to a cell. As the methods of observation improved, it was recognized that, within the developing egg, two vesicles appeared where one only had previously existed, to be followed by four vesicles, then eight, and so on in multiple progression until the ovum contained a multitude of vesicles, each of which possessed a nucleus. ”

“ When the egg is in the ovary and before it is quite mature,—at the time, in fact, when it is receiving nutriment from ovarian cells,—it contains a germinal vesicle including a germinal spot, but when the egg is mature the germinal vesicle has disappeared, and there exists in its place at one portion of the periphery of the egg-contents a cluster of minute bodies called chromosomes by Henking, whom we shall follow in briefly describing their changes. ”

“ In some cases the whole of such a polynuclear mass gives rise to only a single ovum, owing to the atrophy of all the nuclei but one, in others it gives rise by subsequent division to two or more ova, each with a single germinal vesicle.
(5) All the cells of a nest do not undergo the above changes, but some of them become smaller (by division) than the indifferent cells of the germinal epithelium, arrange themselves round the ova, and form the follicular epithelium. ”

“ The small primitive ovum of the bird begins very early to take up into itself a quantity of food-stuff through the yelk-membrane, and work it up into the "yellow yelk." In this way the ovum enters on its second stage (the metovum) , which is many times larger than the first, but still only a single enlarged cell. Through the accumulation of the store of yellow yelk within the ball of protoplasm the nucleus it contains (the germinal vesicle) is forced to the surface of the ball. ”

“ The germinal vesicle of a mammalian ovum being about 1⁄1000 of an inch, mean diameter, might contain five hundred million of gemmules, which, if used up at the rate of one per second, would last more than seventeen years. If the whole ovum, about 1⁄150 in diameter, were all gemmules, the number would be sufficient to last, at this rate, one per second for 5,600 years! ”

“ But the result is the same in all cases—the formation of a (generally spherical) cluster of heterogeneous (originally homogeneous) cells. This stage is called the morula (“mulberry,” which it somewhat resembles in shape) . Then, as a rule, a fluid gathers in the interior of this aggregate of cells; it changes into a spherical vesicle; all the cells go to its surface, and arrange themselves in one simple layer—the blastoderm. The hollow sphere which is thus formed is the important stage of the “germinal vesicle,” the blastula, or blastosphere. ”

“ Then the germinal vesicle became a self-moving, self-acting thing—not at first, but after a series of changes, adapted into the type of the human family, whose life was but the life for ages of the animals that have perished, and are now fossilized in their various formations. ”

“ The description of Kleinenberg (14) for Hydra, and Götte for Bombinator, may perhaps be selected as especially complete in this respect; in both instances the germinal vesicle commences to atrophy at a relatively early period.
Coming to the more modern period the researches of five workers, viz. Bütschli, E. van Beneden, Fol, Hertwig, and Strasburger have especially thrown light upon this difficult subject. ”

“ The first and most important of these facts is that every man, like every other animal, begins his existence as a simple cell. This round ovum has the same characteristic form and origin as the ovum of any other mammal. From it is developed in the same manner in all the Placentals, by repeated cleavage, a multicellular blastula. This is converted into a gastrula, and this in turn into a blastocystis (or embryonic vesicle) . The two strata of cells that compose its wall are the primary germinal layers, the skin-layer (ectoderm) , and gut-layer (entoderm) . ”

“ Its outer layer « 60 » is clear or transparent, and more dense than the inner mass, which seems granular. It has at one end a curious vesicle which can be seen gradually to expand and become filled with a clear drop of liquid, and then suddenly to contract and expel the contained fluid through a series of pores in the adjacent part of the outer wall. This is the so-called pulsating vesicle, and is an organ both of circulation and excretion. In another part of the body may be seen the nucleus, which is a little cell capable, at certain times, of producing by its division new individuals. ”

“ The epithelium may separate from the stratum basale, leaving a red lesion with shreds of torn epithelium. Vesicular fluid may leak through the stratum corneum without the formation of a true vesicle (Seibold and Sharp 1960) . Since vesicles are most often seen at the site of mechanical stress, they usually rupture quickly, leaving a red erosion. Often, lesions are contaminated with dirt and debris (Fig. 25.2) , resulting in infection with opportunistic bacteria. ”

“ A vesicle is first produced, and then a contraction appears around the vesicle, and this contraction increases till a portion of the vesicle is cut off and swims away free like an amœba. The same phenomenon may be observed with vermiform growths, a single seed often giving {141}rise in this way to a whole series of amœbiform or vermiform productions.
It must be remembered that in an osmotic growth the active growing portion is the gelatinous contents in the interior, the external visible growth being only a skeleton or shell. ”

“ In science, we have to consider two things: power and circumstance. All we know of the egg, from each successive discovery, is, another vesicle; and if, after five hundred years, you get a better observer, or a better glass, he finds within the last observed another. In vegetable and animal tissue, it is just alike, and all that the primary power or spasm operates, is, still, vesicles, vesicles. Yes—but [Pg 276] the tyrannical Circumstance! A vesicle in new circumstances, a vesicle lodged in darkness, Oken thought, became animal; in light, a plant. ”

“ The ovum, enclosed by the zona radiata, passes into the Fallopian tube and undergoes a segmentation which has not been studied with great detail. On the close of segmentation, about six days after impregnation, it assumes (Hensen) a vesicular form not unlike that of other Mammalia. To the inner side of one wall of this vesicle is attached a mass of granular cells similar to the hypoblastic mass in the blastodermic vesicle of the rabbit. The egg still lies freely in the uterus, and is invested by its zona radiata. ”

“ Gradually the vesicle becomes larger and of firmer consistence, and now the whole of the wall, except where the cytoblast forms part of it, consists of a jelly. By-and-bye the cell grows beyond the edge of the cytoblast and rapidly becomes so large that the latter appears only as a small body inclosed in one of the side walls. ”

“ Fig. 62. Section through the trunk of a Lepidosteus embryo on the sixth day after impregnation.
mc. medullary cord; ms. mesoblast; sg. segmental duct; ch. notochord; x. subnotochordal rod; hy. hypoblast.
With reference to the features in development, visible in sections, a few points may be alluded to.
[Pg 115] The optic vesicles are very prominent outgrowths of the brain, but are still solid, though the anterior cerebral vesicle has a well-developed lumen. The auditory vesicles are now deep pits of the nervous layer of the epiblast, the openings of which are covered by the epidermic layer. ”

“ Soon after, the cytoblasts are seen as granular coagulations from the granular mass; they grow considerably in this free condition, but as soon as they have reached their full size, a delicate transparent vesicle is formed upon them; this is the young cell, which at first presents the appearance of a very flat segment of a sphere, whose plane side is formed by the cytoblast, the convex by the young cell (the cell-membrane) , which rests upon the cytoblast as a watch-glass on a watch. ”

“ He adds particularly that the cytoblast can never lie free inside the cell, but is always enclosed in a duplication of the cell-wall, and he thinks that it is an absolute law that every cell, except perhaps in cambium, begins as a minute vesicle, and grows to the size which it reaches in its matured state. ”

“ The embryo early becomes a "blastosphere" or hollow vesicle formed of a single layer of cells. One half of this is invaginated, or pushed into the other half, and a "gastrula" is thus developed, the cavity of which is the "archenteron," and the two cell-layers respectively "ectoderm" and "endoderm." The "blastopore," or orifice of invagination, is at the posterior pole of the larva, where it narrows and closes, the locomotor, transverse band of cilia developing round it. No other bands of cilia appear in this form of development. ”

“ But meanwhile a cavity has formed in the midst of the ovum. This makes its appearance at about the eight-cell stage, the eight cells not quite meeting in the centre of the ovum. The central cavity so formed is thus surrounded by a single layer of cells, and it remains as a single layer throughout the process of segmentation, so that there results a hollow vesicle composed of a membrane constituted by a single layer of cells (E.) . ”

“ All three operations were successful, and on the eighth day all three vesicles were matured “like a pearl upon a rose petal,” as Jenner described a perfect specimen. On that day, the eighth day after the operation, I visited my patient, and to all appearance she was in the soundest health and spirits, with her usual bright eyes and ruddy cheeks. Although I was much tempted to take the lymph from so healthy a vesicle and subject, I did not do so, as I have frequently seen erysipelas and other had consequences follow the opening of a matured vesicle. ”

“ The blastodermic vesicle has at first the usual spherical form, but it grows out at an early period, and with prodigious rapidity, into two immensely long horns; which in cases where there is only one embryo are eventually prolonged for the whole length of the two horns of the uterus. The embryonic area is formed in the usual way, and its long axis is placed at right angles to that of the vesicle. On the formation of an amnion there [Pg 251] is formed the usual subzonal membrane, which soon becomes separated by a considerable space from the yolk-sack (fig. 153) . ”

“ Fig. 15 is the same species without the colouring matter, in order to show the shape of the cells. The Pediastrum reproduces by continual subdivision of the contents of each cell into a number of smaller cells, termed “gonidia” on account of their function on the perpetuation of the species. When a sufficient number has been formed, they burst through the envelope of the original cell, taking with them a portion of its internal layer, so as to form a vesicle, in which they move actively. ”

“ When first discovered, extracellular vesicles were merely considered to result from stressed cells shedding waste products [44] . However, after the discovery of nucleic acid sequences in these vesicles, they were considered much more interesting, as this suggested that they might facilitate genetic signaling [33] . sRNA-containing vesicles in human plasma are either shedding vesicles, formed by outward-budding at the plasma membrane, or exosomes, formed by inward budding of intraluminal vesicles (ILV) at endosomal membranes of multi-vesicular bodies (MVBs) . ”

“ Whether the germ-cells appear, as in Hydra, to be derived from the ectoblast, or, as is usually stated, from the endoblast, in neither case ought they to be classed with the internal or external epithelium; they are germ-cells, and the epithelium which they form is neither epiblastic nor hypoblastic, but germinal, forming originally a simple gonocœle, afterwards, in the higher forms, the cœlom with its cells of various function. ”