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B   Mitosis of primary germ cells

Primary germ cells (prespermatogonia) differentiate and have migrated to the embryonic gonads by the fifth intrauterine week. Before the onset of puberty at between 13 and 16 years of age, spermatogonia within the seminiferous tubules of the testis undergo some 30 mitotic divisions. Increased temperature in the testis would be expected to affect this stage of development. The exact mechanism is unknown, but testicular hypothermia is known to be important in normal development of spermatogonia in primates and most other mammals.

Meiosis does not occur until after puberty, when spermatogonia have already differentiated into primary spermatocytes under the influence of testosterone produced by the interstitial cells of the testis. The first meiotic division then produces secondary spermatocytes - haploid cells (1N) but with doubled chromatids (2C). The second meiotic division produces spermatids - haploid cells with single chromatids (1C).

The process of spermiogenesis is the differentiation of spermatids into cells with flagellae and heads, known as spermatozoa or sperms. The term spermatogenesis refers to the entire process of differentiation of spermatogonia into spermatozoa, beginning at puberty.

Differentiation of the mesonephric (Wolffian) ducts into such important male reproductive tract structures as the ductus deferens, ejaculatory duct, and epididymis occurs at the eighth intrauterine week, thus much earlier than the insult in this case.

Degeneration of the paramesonephric (Mòllerian) ducts in the male embryo occurs at the same time, and in any event would have little, if any, effect on male fertility.

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