The first figure represents the Cell at rest, with its cytoplasm containing the Centrosomes, and the Nucleus containing the Chromatin substance. Then we have the Cell in action; and this is due to the action of the Centrosome on the chromatin. The Centrosome divides into two parts (like a Visarga) one of which passes to one pole and the other to the opposite pole of the nucleus. In the nucleus we get the following changes: the Nucleolus disappears, and the chromatic substance becomes aggregated and forms a continuous thread. At the same time a spindle appears between the daughter-centrosomes, and the nuclear membrane disappears.
Then the chromatic thread breaks up into a number of segments called Chromosomes, which arrange themselves (V-shaped) round the equator of the spindle. Then the Chromosomes divide into two equal parts, still at the equator of the spindle. After this the halves of the chromosomes move towards the opposite poles of the spindle, in the vicinity of the centrosomes, and arrange themselves in the form of an arc of a circle (like an Anusvara) At this stage constriction appears at the level of the equator of the spindle. In the end, this constriction deepens and the cell is divided into two equal halves, the daughter-cells.
The Ovum or the Female Cell: We have so far considered the Cell in its process of maturation, without reference to the conjugation of the male and the female. It is necessary now to consider this aspect of the question. The Ovum or the female cell presents all the structural features of the animal cell; but it is peculiar on account of its relatively large size, the large size of its nucleus, and the possession of an investing membrane between the lines of the nuclear and the cytoplasmic regions.
Maturation of the Ovum: The Centrosomes play a most important part in the maturation of the Ovum. As in the case of the animal cell in general, they separate, pass to the two poles of the nucleus, form a spindle, and act on the chromatin. The latter form into chromosomes, then divide into two halves and are attracted to either polar end. The rotating spindle then forms a projection at one polar end. Starting from the position of rest, there are four stages of development, at the end of which a new cell is formed. It is then separated and projected out of the main body of the ovum to the investing membrane. This separated cell is called a Polar Body. In like manner a second polar body is formed and projected out; at the same time the first polar body divides into two. Thus there are three Polar Bodies (or small cells); the main body of the cell, the fourth, is the mature Ovum, which may be conjugated with the male seed.
Spermatozoon or Male organism: A Spermatozoon is a minute male organism or cell. It is one of the smallest known cells, frequently being no more than one hundred thousandth of the size of the ovum or the female cell. It is produced in enormous quantities and, relatively to other minute cells, is extremely tenacious of life. The process of its maturation is akin to that of the animal cell in general.
This figure shows the division of the Spermatocyte or Male Cell into four Spermatids, even as the Ovum divides into four the mature Ovum and three Polar bodies. Only one Spermatid unites with the mature Ovum, the remaining three Polar bodies and three Spermatids, though present, do not appear to act.
Fertilization: Fertilization is the union of the male with the female gamete or cell, and the conjugated ovum is called a zygote. The zygote has the same form as the mature ovum.
As has been pointed out, the primary spermatocyte (male cell) divides into four spermatids in its process of maturation, even as the primary oocyte (female cell) divides into four, three polar bodies and the mature ovum. But in the conjugation between the male and female cells, the union takes place between the mature ovum on the one hand and only one spermatid on the other. The remaining three spermatids and three polar bodies are present but do not appear to function; and it may be said that out of four parts on either side the union takes place between one of each only, and out of their union a new creature is formed.
The Centrosomes play a most important part in the process of fertilization. They accompany the male germ which enters the mature ovum, and it is their action which brings about the division of the zygote (conjugated cell). The zygote divides into two then subdivides into four, and so on, till the whole cell, including the investing membrane, is filled with a number of cells. These cells arrange themselves in different groups and form three layers out of which the various parts of an organism are developed.
Embryo: An embryo may be defined as a multi-nucleated protoplasmic mass.
Reproduction of Animals: Reproduction of animals is of two kinds, (a) Asexual, and (b) Sexual.
Asexual Reproduction: There are a number of cases among both plants and animals where, if the whole body be cut in pieces, each portion may grow into a new complete organism. This is asexual reproduction.
Sexual Reproduction: Sexual reproduction may be defined as the production of a new organism from a zygote or fertilized ovum. In true sexual reproduction the conjugation is heterogamous, i.e., the gametes or cells are unlike, that is, male and female. The fusion is chiefly nuclear.
A Special Case: Parthenogenesis: A special case of reproduction, called Parthenogenesis, may be distinguished. Parthenogenesis is the production of a new organism from, the female organism, without its previous conjugation with the male gamete. But it is to be regarded as secondary to and degenerate from true sexual reproduction.
According to another view, however, "it appears that there is some evidence to show that ova, which in normal condition are incapable of development without fertilization, may yet develop if subjected to an altered environment Experiments made in this connection appear to suggest that the ova have the power of development, but are not able to exercise it in their normal surroundings. There is reason to believe that the same assertion may be made of spermatozoa (male tells). However, phenomena of the nature of Parthenogenesis have never been observed in the male gamete".
Science and Philosophy: If we were to construct a new scheme of thought in regard to the creation of life based on the observed facts of modern Biology, the following would be some of its principal features:
1. All life is created in the following ways:
- From the physical union of the Male and the Female, corresponding to the union of the male and female cells;
- By means of natural separation from the parent, as in the case of many plants and animals;
- From the female alone, without its previous union with the male, as is alleged to be in a case of Parthenogenesis;
- From the male alone, without its previous union with the female, as is possible in another case of Parthenogenesis.
2. Further, considering the processes of maturation and fertilization, we should say that when creation takes place, the one becomes four, both male and female, and a new creature is born of the union of the fourth part of each, the remaining three parts of each being apparently inactive. Also, that there are four stages in the development of life, which becomes manifest in the fourth stage.
3. A scientific scheme of thought would take note of the form of the Cell, male and female, both at rest and in action, and hold that the first constituent of life is a fluid or watery substance that its form is elliptical that this ellipse has a rounded and a pointed side like an egg that creation takes place from the pointed side. Further, we should have to consider the action of the Centrosome on the nucleus, and say that there is an energy of mysterious power which, acting on the central part of life, (nucleus of the Cell) develops, divides and multiplies it; that it is like a point, which breaks into two; which has a radiating power; which is magnetic in its action; and it is this energy which is the supreme creative energy of life.