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Gemmule
"Gemmule" in a Sentence (25 examples)
A very similar mode of growth and propagation is found among the compound Polypes, whose gemmules, like those of the Medusæ, are at first free, and moved by cilia; afterwards attached, and budding forth with a plant-like body.
Accidental hematozoa may be found, […] in the vessels of man and other animals; these are foreign to the blood, and do not circulate with it. The hydatid, acephalocystis endogena, detaches its gemmules from its inner surface; one thus inclosing the other in a series, like pill-boxes. It is found in the liver, kidney, womb, etc.
They [spores and tetraspores] may rather be considered, the one a true spore, supposed to be fertilized by means of an antheridium; the other, a mere gemmule, or bud of the simplest possible structure, which is cast off by the parent plant, and carries with it sufficient vitality to become the nucleus of a fresh individual.
The gemmules of the Marchantia [a genus of liverworts] are little disc-shaped masses of cells composed of two or more layers.
The ova [of the brown hydra, Hydra oligactis, formerly Hydra fusca] covered with a horny substance possess a great power of resistance to the cold, thus preserving their vitality until the return of conditions favorable for their existence, when development begins to take place. This proceeds up to a certain point, the covering of the ovum bursting, liberates the embryo, which becomes ciliated, and for some time swims freely in the water; in this condition it is known as a "gemmule."
Sponges are propagated by gemmules, which originate in the organic mucus, and are carried out of the body by the effluent currents just described. In some sponges these gemmules are ciliated and locomotive when mature; but it seems probable that the majority of the species produce only unciliated gelatinous grains, which are nevertheless endowed with a very active motility, like the ultimate particles of even inorganic matter.
The increase in size of the gemmule takes place by means of cell growth and division, and by the fusion of neighboring small gemmules.
The green fresh-water sponge dies away in autumn, all but little pinhead clusters of cells called gemmules, which eventually float away from the dead skeleton and start new sponges in the spring.
All fresh-water and some marine sponges reproduce asexually by means of gemmules; these embryos are formed simply by assembly of a few amoebocyte cells. Reproduction is also accomplished sexually by the union of sperm and egg cells.
The actual formation of gemmules by fresh-water sponges is so clearly an adaptation to seasonal climatic changes, that at first it was reasonable to believe that seasonal alternation itself induced the gemmulation. However, conflicting reports on the relationship of gemmule production to seasonal temperature changes required that an alternative hypothesis be developed.
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Asexual reproduction in the sponge begins with the formation of small particles, known as gemmules, within the parent sponge tissue. […] Gemmule formation has been studied in a number of species, especially in E. fluviatilis[…], as gemmule formation can be induced in vitro[…]. Specific stages in the process of gemmule formation have been proposed based on the time-lapse microscopic study of Rasmont and De Vos (1974).
[…] I assume that cells, before their conversion into completely passive or "formed material," throw off minute granules or atoms, which circulate freely throughout the system, and when supplied with proper nutriment multiply by self-division, subsequently becoming developed into cells like those from which they were derived. These granules for the sake of distinctness may be called cell-gemmules, or, as the cellular theory is not fully established, simply gemmules. […] Their development is supposed to depend on their union with other partially developed cells or gemmules which precede them in the regular course of growth. […] Lastly, I assume that the gemmules in their dormant state have a mutual affinity for each other, leading to their aggregation either into buds or into the sexual elements.
Curse you, you wandering gemmule, / And nail you fast in Hell! / You gave me gout and bandy legs, / You beast, you wanted a cell! / Gout, and gravel, and evil days— / (Theology speaks, shaking her head) / But there is One who knows your ways!
This theory [of pangenesis] appears to be as follows: That each living organism is ultimately made up of an almost infinite number of minute particles termed "gemmules," each of which has power to reproduce its kind. […] That such a complete collection of gemmules is aggregated in each ovum and spermatozoon in most animals, and in each part capable of reproducing by gemmation (budding) in the lowest animals and in plants. Therefore in many of such lower organisms such a congeries of ancestral gemmules must exist in every part of the body, since in them every part is capable of reproducing by gemmation.
According to this hypothesis [pangenesis], every unit or cell of the body throws off gemmules or undeveloped atoms, which are transmitted to the offspring of both sexes, and are multiplied by self-division. They may remain undeveloped during the early years of life or during successive generations; their development into units or cells, like those from which they were derived, depending on their affinity for, and union with, other units or cells previously developed in the due order of growth.
Metamorphosis, in this respect, may truly be described as a process of the readjustment and rearrangement of the atoms and gemmules of the insect's frame. The variations of living beings may, in their turn, be explained by assuming an irregularity to exist in the arrangement of the gemmules which unite to form the germ of the varying form. Modified cells will give out modified gemmules, and these last will produce variations in the new being.
[M]icroscopic research has so far failed to discover any trace of Darwin's Gemmules in the blood or anywhere else. Furthermore, sheep have been docked in early life for scores of generations, yet every lamb is born with a tail. Since both parents and all of their ancestors have been docked, whence come the gemmules to produce the tail in the lamb?
In retrospect, there were three main defects of Darwin's "pangenesis" theory of inheritance: (1) the presumption that there was a gemmule corresponding to every trait and specific to one and only one trait; (2) the idea that copies of all gemmules are transmitted to the next generation; and (3) the idea that somatic changes occurring during the lifetime of an individual could locally alter gemmules proceeding from the affected organ and then be passed to subsequent generations via gemmule replicates contained in the gametes.
To what do this cavity which contains the gemmule, this thin layer which covers it, correspond? We have stated that the cotyledon is nothing else than the first leaf of the little vegetable, and the gemmule the union of the leaves which will follow it.
The embryo is composed of cells and spiral vessels; a small stem, or stalklet; a rudimentary descending portion, which becomes the root or radicle; and a rudimentary ascending axis, surrounded by a bud, or gemmule. Between the radicle and the gemmule, the first leaves developed are termed cotyledons: a plant having leaves like seed-lobes.
The incipient apical meristem (gemmule) is located between the two cotyledons of the mature embryo and consists of a pocket of approximately 200 meristematic cells[…].
Concussion from shell explosion often sufficient to produce miliary hemorrhages in brain substance. Mott has found such lesions in brains of shell shock. Lesser lesions on fine nerve fibrils and gemmules, or nerve cells may reasonably be postulated.
The mitral cells also extend several secondary dendrites (SD) laterally outward into the external plexiform layer (EPL), where they are in intimate association with the dendritic spines (or gemmules) belonging to the dendrites of the granule cell population, whose cell bodies (g) lie deeper in the granular layer (GRL) of the bulb.
Two GAD-positive gemmules (D₁, D₂) from dendrites of periglomerular neurons form synapses with a mitral/tufted dendritic shaft (D₃). One gemmule (D₁) appears to form a reciprocal synapse, and the other gemmule (D₂) appears to be presynaptic only (original magnification × 54,000).
There is both ultrastructural and electrophysiological evidence indicating that the mitral/tufted dendrite-to-gemmule synapses are excitatory, whereas the adjacent gemmule-to-mitral/tufted dendrite synapses are inhibitory.
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