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Updated: July 10, 2025
I do not suggest that the colour and markings of a species or variety were, in all cases, due to external conditions, but if the effect of external stimuli can be inherited, can affect the chromosomes, then the evidence concerning unit factors no longer contradicts the possibility of a character gradually increasing, under the influence of external stimuli acting on the soma from zero to any degree whatever.
A factor in Mendelian experiments usually affects only one organ or one part of the organism. The factor for double hallux in fowls, for instance, may coexist with single comb or rose comb. The general impression produced on the mind by study of Mendelian phenomena is that the organism is a mosaic of which every element corresponds to a separate element in the chromosomes.
If this egg should now unite with the other reproductive cell from the male, the resulting fertilized egg would plainly contain a number of chromosomes larger than that normal for this species of animal.
All the cells of the body, assuming that somatic segregation does not occur, must possess the same chromosomes as the zygote from which it developed, and whether the sex chromosomes are XX or XY or X, there must be at any rate one chromosome bearing the factor for milk glands.
We may call this reduced number N and the full number 2N. The ova developing by parthenogenesis and giving rise to males segment in the usual way, and all the cells both of soma and gametocytes contain only N chromosomes.
For the time being, let the feminists glory in the fact that they have two more chromosomes to each cell than their opponents. Certainly there can be no talk here of a natural inferiority of women. Yet the matter is after all not so simple as this would make it out to be. All that can be safely laid down is that the character of the reproductive organs is determined by the extra chromosomes.
In the female two of these are visibly different from the rest, while in the male there is one odd one, the remaining 20 being like the corresponding 20 of the female. Before the germ cell becomes fit to mix with a germ cell of opposite sex, in the process of fertilization, it must lose one half of these. So the number of chromosomes for the species is kept the same or constant.
It may occur, as described, at about the time the asters have reached the opposite poles of the nucleus, and an equatorial plate is formed. It is not infrequent, however, for it to occur at a period considerably earlier, so that the chromosomes are already divided when they are brought into the equatorial plate.
The study of the development of the spermatozoon shows that it has come from cells which contained the normal number of four, but that this number has been reduced to one half by a process which is equivalent to that which we have just noticed in the egg. Thus it comes about that each of the sexual elements, the egg and the spermatozoon, now contains one half the normal number of chromosomes.
In man, two X-chromosomes have been discovered, half the sperm containing 12, and the other half containing only 10 chromosomes. The number of chromosomes in human cells consequently is 22 in the male and 24 in the female. The X-chromosome is the bearer of sex destiny. There still remains the work to be done on the actual control of sex by man, apart from its natural determination.
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