There is a part called the Centrosome observable in many cells, and this is made up of one or two minute dots surrounded by a radiating aster called the Attraction-Sphere.
The centrosome is concerned in the process of cell-division and in the fertilization of the ovum; it is an important organ in the production of cell from cell, though its full nature and function are not yet known.
The aster commonly disappears and the centrosome persists, usually outside the new nucleus, but sometimes within it.
The centrosome is one in the beginning, but before dividing the cell it divides itself into two persons, so that one of the centrosomes may accompany each of the two cells.
When the centrosome divides the cell, two cells are produced capable of reproducing themselves in like manner.
Each centrosome seizes one half of the brain of the parent cell thus divided and draws it to one side of the cell to form the nucleus of one of the new cells.
The name has been used both as excluding and including the centrosome, and also to designate a modified mass of protoplasm about a centrosome whether aster rays are developed or not.
The central mass of an aster from which the rays extend and within which the centrosome lies when present; the attraction sphere.
Meves, however, maintains the possibility that the numerous centrosomes appearing in the egg arise by the rapid fragmentation of a centrosome already present.
In many other cases the reverse of this condition occurs, the centrosome dividing long before there is any indication of division in the nucleus (e.
Boveri (1903); by shaking the egg shortly after fertilization the sperm centrosome is prevented from dividing, and a monaster instead of a diaster results, the divided chromosomes remaining in the one nucleus.
Some of the fibrillae in the latter region become attached to the chromosomes and are termed "mantle fibres"; others become continuous from one centrosome to the other and constitute the "spindle fibres.
Yet a centrosome appears later in the nucleus of the swarm spores and migrates into the cytoplasm.
In almost all cases the centrosome of the resting cell, when this can be detected, lies in the cytoplasm, and is often already divided in preparation for the next mitotic division (e.
For Schaudinn has shown in Acanthocystis that, in the formation of the swarm spores, the nucleus divides amitotically, the centrosome remaining visible and unchanged at the centre of the radiating processes.
In some cases the flagella are in direct connexion with the centrosome (see below, Cell-division), e.
Trypanosoma and spermatozoa, in some cases even while the centrosome is functioning in mitosis (e.
This indifferent nuclear or cytoplasmic position for the centrosome is paralleled by the attraction sphere or homologue of the centrosome in many Protozoa.
Heidenhain in relation to the leucocytes of the salamander, in which there is a permanent centrosome and astral rays to which the contractile movements of the cell appear to be due[24] (fig.
If this is true, the centrosome of the zygote nucleus must be entirely derived from that of the male pronucleus.
The general rule appears to be that the female pronucleus is without a centrosome, and that no centrosome appears in the female in the divisions by which the gamete arises from the progamete.
The centrosome now divides, the membranes of both nuclei disappear, and a spindle is formed.
Before the head of the spermatozoid which has entered, appears a centrosome (Fig.
When the cell commences to divide, the meshes of the network of chromatin contract and the centrosome divides into two parts (Fig.
Some of these rays extending in the direction of the chromosomes, become attached to one of their extremities and draw it toward the corresponding centrosome (Fig.
The chromosomes then form a new meshwork of nuclear chromatin, and we have then two cells each with a nucleus and a centrosome like the mother cell (Fig.
Thus around each centrosome are grouped as many chromosomes as the mother cell possessed itself (Fig.
A later stage, showing elongation of nuclei, centrosome and sphere at posterior end.
In the later stages the centrosome is clearly seen at the base of the head (fig.
The centrosome which, although small, is conspicuous in each mitosis, is seen in figure 83 between the two parts of the spindle-remains, applied to the outside of the nuclear membrane.
Anaphase of first maturation mitosis, one centrosome divided.
The centrosome was also conspicuous in all of the cells of this group.
Does the magic of the centrosome correspond in some sense to the glamour, so well known in human affairs?
At this stage, then, we have a tiny, starlike centrosome at each end of the cell, and a transverse line of chromosomes between.
The centrosome which lies passively at the side of the nucleus in the typical cell (Fig.
Regarding the nucleus as a tiny globe, we may say that the chromosomes lie in the equatorial plane, while the two parts of the centrosome move towards the North and South Poles respectively.
The chromosomes range themselves in a belt across the centre of the nucleus, and the centrosome breaks into two parts, which take up a position one at each end of the nucleus.
No fusion of any number of such cells can therefore lead to any further change or growth, for growth is based on cell division, and the centrosome is the organ of division.
From each centrosome extremely delicate lines may be seen to radiate in two directions.
On either theory we may assume that they indicate an influence, emanating, it may be, from the centrosome and capable of being exercised both on the cell plasm and on the nucleus contained in it.
As from the centrosome at the pole of the spindle both sets of radiations diverge, it is not unlikely that it acts as a center or sphere of energy and attraction.
On the dynamical theory, the chemical and physical energy in the centrosome might influence the cell plasm and the nucleus and attract the chromosome elements of the nucleus to the poles of the spindle.
In the center of each pole is a somewhat opaque spot (central body) surrounded by a clear space, which, along with the spot, constitutes the centrosome of the sphere of attraction.
If there is only one it soon divides into two, and if it has already two, this is because a single centrosome which the cell originally possessed has already divided into two, as we shall presently see.
From it radiate the forces which control cell activity, and hence this centrosome is sometimes called the dynamic center of the cell.
The egg centrosome has divided, and the male cell with its centrosome has entered the egg.
In some cases, and this is true for the worm we are describing, it is certain that the egg centrosome disappears while that of the spermatozoon is retained alone to direct the further activities (Fig.
The centrosome divides as in ordinary cell division (Fig.
The fundamental feature, of nature's machine building is thus based upon the machinery of the nucleus and centrosome of the organic cell.
In the activities which characterize cell life this centrosome appears to lead the way.
The centrosome has divided, and the two pronucleii have been brought together.
Plainly, we must conclude that the chromatin material is something of extraordinary importance to the cell, and the centrosome is a bit of machinery for controlling its division and thus regulating cell division.
It is not yet certain, however, whether the centrosome is a constant part of the cell.
Again the discovery of the centrosome as a distinct morphological element has still further added to the complexity of the life substance, and proved that neither nucleus nor cell substance can be regarded as the cell or as constituting life.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "centrosome" in a variety of sentences. We hope that you will now be able to make sentences using this word.
