She sat down, and I sat beside her, and we talked of children.

She said — and until that moment she had neither child nor son:

"How I should love to have a beauti-ful baby girl born to me... but I want her fair-skinned, with blond hair."

I looked at her with the eye of a careful examiner: gray had already traced its first lines at the sides of her head, though she had not yet crossed the threshold of twenty-five; her hair was jet-black, like the hair of that "orphan girl" of whom the poet sang, immortalizing her though not himself; and she was, moreover, as dark as the soil from which she was created. So I asked her:

"Do you really expect the newborn to be a girl... and blond-haired into the bargain?!"

She found my question strange and said:

"Why not?! Is there anything to prevent it?"

I smiled the smile of one who knows the matter as it truly is, then answered her:

"Nature may object... or may not object at all. And before I settle the matter, I should like to put to you these basic questions. First: has anyone in your family, regardless of sex, ever had blond hair?"

She said, "No."

"Then: does your husband, or anyone in his family, have blond hair?"

She answered no again. So I asked her once more:

"How, then, do you want an unreasonable thing to come true?"

She was taken aback by this firm verdict, coming before she expected it, and demanded explanation and interpretation; so I began to tell her this tale of mine.

First, you want a girl... Very well. That may happen and may not, and either outcome is possible at a rate of fifty percent. That is, you have half a chance that half your wish will come true. And this, in any case, depends on circumstances — or rather on chance. If chance wills it, you shall have a baby girl; and if it does not, your affair rests with God.

To make the matter clearer to you, I shall relate the precise operation by which nature determines the sex of the newborn — so that when one of you bears a boy she will not lift her nose in pride and grandeur, and when one of you gives birth to a girl she will not shrink into herself in shame and embarrassment. For

the fault in that is not hers; nor was the newborn a girl because God answered the prayer of the mother-in-law or the husband's sister. The fault, if it is to be counted a fault, is the fault of chance — that mysterious power that rules everything that passes along the paths and crossroads of life.

Before the child is born, it is an embryo. Before that, it is a cluster of living cells that multiply with time until they become that embryo. And before that state, the cluster is a single cell, composed of the fusion of two cells, each distinguished from the other by its shape, by the kind of work it performs in creating the new being, and by the origin from which it arises. These two cells are reproductive cells — that is, of the class that has taken upon itself the task of preserving the human species. One is large and is carried by the woman: we shall call it "the female cell." The second is small and is produced by the man: we shall call it "the male cell."

The female cells in a woman are alike in structure, with no distinction between one and another. Each is composed of the cell's heart (or its nucleus) and of nutritive matter heaped around that heart. In the heart are fine threads, like pieces of short rope, called chromosomes; in every reproductive cell there are twenty-four of them.

The male cells, however, differ in structure within one and the same

person, and they are of two kinds:

1. A cell carrying the trait of femaleness, which we shall name "the X cell."

2. A cell that does not carry this trait, which we shall call "the deficient cell." These cells of both kinds are very small in size; each consists of a heart surrounded by a thin membrane, with a fine hair at its rear like a tail, and these cells are able to move and swim in the fluid they are in by moving that fine tail.

We now have three kinds of reproductive cells: the female cell, the X cell, and the deficient cell — the first in the woman, the latter two in the man.

The female cell (in the woman) resembles the X cell (in the man) in that each of them has a set of traits that has no coun-terpart in the deficient cell. This set is concentrated in a special chromosome known as the X chromosome, which is present in both of the two similar cells. When these two chromosomes come together, the similar traits come together as well, and this happens only through the meeting and fusion of the two cells mentioned. Then a new creature is formed possessing the marks of femaleness — that is, one of the fair sex. Thus the baby girl results from the blending of the X cell with the female cell.

But the matter may not proceed along this line. If the deficient cell — which carries, instead of the X chromosome, another chromosome — fuses with the female cell, we then have only one set of those special traits (that is, a single X chromo-some), and this is not enough to supply the sexual traits that would make the new creature a female; hence this fusion yields a male embryo. Thus we see that the boy results from the blending of the deficient cell with the female cell.

Who, then, governs the meeting and blending of the cells in the manner we have set forth?

The man supplies both kinds of his cells — the X and the deficient. The woman supplies her single cell, the female cell, and this passive cell remains ready to catch the first of the male cells that rush toward it as