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In other words, the genetic power of the fertilized ovum weakens, the more it is spread over the growing mass of the tissues of the embryo; but, while it is being thus diluted, it is concentrating anew something of itself on a certain special point, to wit, the cells, from which the ova or spermatozoa will develop.
The young gentlemen had developed many pleasing traits of character during the comparatively short period during which he was brought into public notice as one of the passengers of the ill-fated Nancy Bell; but in none of these had he so well exemplified his natural and ingenious bias of mind as in the little predilection, if it may be so termed, for bird slaughter in ovum, which first saw the light in Kerguelen Land.
Unless some arrangement was made to prevent it, the act of fertilization would cause the number of chromosomes in the fertilized ovum to be double the number characteristic of the species.
Primary purpose of sex in the human race Life is the result of union of two forces Birth the same in human beings as in other forms of life Process of conception in female How female ovum is fertilized by male When puberty begins and ends in women.
Through the veins it returns to her heart, by which it is distributed through the arteries to the various regions of the body. The tiny lakes, in which the villi hang, are thus made a part of the mother's circulation and as such are regularly replenished with purified blood. By this means the ovum receives a rich supply of nutriment, and as a natural consequence its growth is rapid.
The remarkable fact is that from this fertilised ovum or zygote is developed usually an individual of one sex or the other, male or female, other cases being comparatively exceptional, although each act of fertilisation is the union of the two sexes together.
When thin slices of the placenta are magnified they are found to contain countless numbers of tiny, finger-like processes; these are the villi, and they constitute the major portion of the organ. The villi seen in a mature placenta are the same as those which projected from the capsule of the young ovum, but not these alone, for many branches have sprouted from the original projections.
The cell derived from the father is always male as goes without saying, we might add, if we knew little of the subject. But the ovum, the cell derived from the mother, may carry either femaleness or maleness. When an ovum bearing maleness meets the invariably maleness-bearing sperm, the resultant individual is a male, of course, and he is male all through.
Furthermore, it is especially important about the time when a menstrual period would ordinarily be expected to be guided by this impulse not to be active, since overexertion then, more than at other times, is apt to be followed by miscarriage. Except in rare cases the observance of this precaution is less urgent after the fourth month, when the ovum has become more securely attached to the womb.
That there is a close connection between the two events seems undoubted; that they are in relation of cause and effect seems likely. It is quite evident that an artificial stimulus can in certain cases set up segmentation, but never can it cause the fertilisation of the ovum.
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