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

 第二步
初级精母细胞不按其他细胞复制的方式那样复制自己，而是以一种独特的方式分裂。可以说，它分裂成两半，分配给两个新细胞各22条常染色体，一条X性染色体给方，一条Y性染色体给另一方。这两个新的细胞叫次级精母细胞，每一个只含有所有其他体细胞一半的染色体（23条）。

The Internal Sex Organs: The Testicles

The Second Step
The primary spermatocyte does not duplicate itself the way all other cells do, but divides in a unique way: It splits in half, as it were, allotting 22 chromosomes plus 1 X chromosome to one of the new cells, and 22 chromosomes plus 1 Y chromosome to the other. The two new cells are called secondary spermatocytes, and each of them contains only half as many chromosomes (23) as all other body cells.