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Can the fatherless brood be reared to maturity and again made to yield a fatherless generation? What is the precise structure of the nuclei of the cells which originate from the nucleus of the egg-cell only, and not from a nucleus formed by the fusion of that with a sperm-cell nucleus? These and similar questions are the motive of further careful study now in progress.
It is a division into polarized duality, psychical and physical, of the human being. It is the great vertical division of the egg-cell, and of the nature of man. Then, this division having taken place, there is a new thrill of conjunction or collision between the divided nuclei, and at once the second birth takes place. The two nuclei now split horizontally.
Thus it is true that the individuals "budded off" or separated by fission from an asexual parent can be ultimately traced through one or more generations of previous asexual parents to an egg-cell produced and fertilised in the regular way, and with this important modification Harvey's dictum is justified.
This egg-cell is differentiated, after fecundation, in gradual and imperceptible transitions, farther and farther, higher and higher, until the individual has reached its perfect organization. No organ, no function of the body, no power or function of the soul or of the mind, appears suddenly, but all in gradual development.
That individuals originate new individuals of their species; that the fecundated germs, if the necessary conditions are present, develop themselves out of the first germ and egg-cell in continually progressive and distinct differentiations, each after its kind, into the full-grown condition, so that individuals endowed with a soul and intellectual life are also developed out of such beginnings; these are facts which are continually repeated before our eyes, and men of science have not yet reached the end in pursuing the actual in these processes into its finest ramifications.
Very briefly, the sperm-cells, which are active, freely moving units, swarm round the egg-cell and one of them eventually enters it. The essential part of the cells, namely the nuclei, coalesce into one nucleus, and an active process of cell division and multiplication is at once started. The single cell divides into two daughter cells, then again into four, and so on.
Provided the requisite conditions for such development are met, these cells are capable of developing into human beings. Each of these remarkable units is called an Ovum, or egg-cell, and represents one variety of the germinal cells. But the other variety, represented by the Spermatozoon and developed only in the male sex, is also required for the production of a human being.
The origin and development of the blastoderm or germinal disc has nothing to do with recapitulation of the phylogeny. It is not the case that the embryos of higher vertebrates are indistinguishable from one another. Even the egg-cell has a specific character, and is totally different from any unicellular organism at the Protistan level.
The important conclusion is forced upon us by these experiments with a needle, that even in so typical and highly organised a creature as one of the higher or five-fingered, air-breathing vertebrates, the egg-cell does not require any material admixture from the sperm-cell in order that it may successfully germinate and develop, but only a disturbance of equilibrium, which can be administered as well by a needle's point as by a sperm-filament!
Let me hasten to add that the miraculous feat was not accomplished with an adult fish. On the contrary, it is found necessary to take the subject quite at the beginning of its career, when it consists of an egg-cell in the earliest stages of proliferation. Considering its potentialities, the egg-cell, seemingly, is as much entitled to be considered an individual as is the developed organism.
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