性器官-男性性器官
The Sex Organs - The Male Sex Organs

内部性器官-睾丸：精子的产生

第一步
精子产生的第一步始于生精小管最外层的细胞。这些细胞称为原始的精原细胞，它们与体内的其他细胞一样，含有46条染色体，包括一条X染色体和一条Y染色体。通过细胞分裂的方式，单个的原始生精细胞可以形成两个同样的姊妹细胞。姊妹细胞中的一个替代了原初的细胞，而另一个则移向生精小管的中央。后者被称为初级精母细胞。

The Internal Sex Organs-The Testicles: The Production of Sperm

The First Step
The first step begins with the cells that lie closest to the outer edge of the tube. These cells are called primitive spermatogonia and, like any other cell in the body, they have 46 chromosomes, including an X chromosome and a Y chromosome. By means of cell division a single primitive spermatogonium forms two new identical daughter cells. One of these takes the place of the original cell, while the other moves toward the center of the tube. This latter cell is called the primary spermatocyte.