United States or Christmas Island ? Vote for the TOP Country of the Week !
Instead of saying that the zygote composed of ovum and spermatozoon is incapable of giving rise in the male to ova, or in the female to sperms, we should hold that the gametocytes ultimately give rise to ova or to sperms according to the metabolic processes set up and maintained in them through their successive cell-divisions under the influence of the double or single X chromosome.
As, further, each human individual has inherited certain personal features from each parent, we must suppose that in the act of conception pieces were detached from their souls and transferred to the embryo. A piece of the paternal soul goes with-the spermatozoon, and a piece of the mother's soul remains in the ovum.
It may very likely produce the same change in the membrane that is caused by the entrance of the spermatozoon under normal circumstances membrane formation may be necessarily coincident with the liberation in the egg of some zymose which arises from a pre-existent zymogen.
The X sex-chromosome is not in itself either female or male, since, as we have seen, either ovum or spermatozoon may contain a single X chromosome. The ovum then with one X chromosome or one X and one Y changes its sex at the next reduction division and becomes male.
You remember I mentioned that at various times during the month an ovum or egg leaves the ovary and passes along the tube to the uterus. Here it remains if it is impregnated or fertilized by a union with the spermatozoon or male element. The whole body of the babe is developed from the ovum or female element after it has been fertilized by the spermatozoon or male element.
There is far more of all these things common to the impregnate ovum and the ovum immediately before impregnation, or again between the impregnate ovum, and both the ovum before impregnation and the spermatozoon which impregnated it.
The spermatozoon penetrates into the ovule and becomes fused with it. The processes of development begin at once to occur. There is congestion of the uterine mucous membrane out of proportion to the rest of the uterus; the ovum finds lodging here, and becomes surrounded by a membrane which incloses it in a separate sac. Pregnancy Defined.
Sexual reproduction is quite a distinct matter. Here, in all these cases, what is required is the detachment of two portions of the parental organisms, which portions we know as the egg and the spermatozoon. In plants it is the ovule and the pollen-grain, as in the flowering plants, or the ovule and the antherozooid, as in the flowerless.
Shortly after leaving the ovary the ovum must receive the stimulus to live and grow; otherwise it will quickly wither and die. This vital stimulus can be imparted only by the spermatozoon. The male germinal cell is like the female cell in the possession of a nucleus; in other respects it is very different.
In parthenogenetic ova this happens without conjugation with a spermatozoon at all: in other cases, since the zygote is compounded of spermatozoon and ovum, we can only say that in the XX zygote, the ovum developing only ova, the female is dominant, in the X or XY zygote developing only spermatozoa the male is dominant.
Word Of The Day