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Updated: June 29, 2025
But we are still some way off any assurance that the main object of the spermatozoon in inducing the development of the egg is this surface alteration.
Within these lobules the spermatozoa are formed by a complex process of cell division and cell germination upon whose description we need not enter here. The spermatozoon may be described as the male sexual cell whose function is to fertilize the female ovum. The spermatozoon is about 1/20 of an inch in length and consists of a head, body and a vibratile tail.
This theory, however, is still open to the objection that the female gametes before fertilisation, and half the male gametes, have the half quantity of sex-chromatin which by hypothesis determines the male condition, so that here again we have the male condition as something which is distinct from the characteristics of the spermatozoon. But if this is the case, what is the male condition?
We have here evidently a process corresponding to the fertilization of the egg in higher animals; yet there is no egg, spermatozoon, or sex. It is a little mass of protoplasm containing a nucleus, and corresponds, therefore, to one of the cells, most closely to the egg-cell or spermatozoon of higher animals.
Consideration of these facts renders apparent the impossibility of fixing with certainty the date of the beginning of pregnancy, since conception may result from the union of the ovum liberated at the beginning of the period with the spermatozoon introduced at the end of that time; or it may result from the meeting of the male elements already within the oviduct with an ovum discharged a day or two before the occurrence of the menstrual period.
From the moment when the spermatozoon penetrates and fecundates the ovum, the fate of the future being is settled by their disposition. The seal of his destiny is soaked with their substance. Every particle of protoplasm, every granule of the impregnated ovum carries the representatives of the parental ductless glands.
Above all we are entitled to ask why there are any effects, or even why there is any ovum or any spermatozoon or curious physiological investigator, to give the artificial stimulus.
The egg is very much larger than the spermatozoon, and contains enough yolk material to afford nourishment for the embryo for a number of days. Within the ovum there are taking place some of the most marvelous changes in the whole life history of the individual. The nucleus of the fertilized egg, and the protoplasm which surrounds it, divide into two cells, then into four, eight, sixteen, etc.
In the cases where the process has been most carefully studied, the further changes are as follows: The head of the spermatozoon, after entrance into the egg, lies dormant until the egg has thrown off its polar cells, and thus gotten rid of part of its chromosomes. Now the centrosome, which is beside the male pronucleus, shows signs of activity.
In man, for example, the addition of twenty-four chromosomes from the spermatozoon to an ovum that already contained twenty-four chromosomes of its own would mean that after fertilization the ovum contained forty-eight.
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