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 Source: Kaplan Anatomy (Embryology) SPERMATOGENESIS At week 4, primordial germ cells arrive in the indifferent gonad and remain dormant until puberty. • When a boy reaches puberty, primordial germ cells differentiate into type A spermatogonia, which serve as stem cells throughout adult life. • Some type A spermatogonia differentiate into type B spermatogonia. • Type B spermatogonia enter meiosis I to form primary spermatocytes. • Primary spermatocytes form 2 secondary spermatocytes. • Secondary spermatocytes enter meiosis II to form 2 spermatids. • Spermatids undergo spermiogenesis, which is a series of morphological changes resulting in the mature spermatozoa. OOGENESIS At week 4, primordial germ cells arrive in the indifferent gonad and differentiate into oogonia. Oogonia enter meiosis I to form primary oocytes. All primary oocytes are formed by month 5 of fetal life; they are arrested the first time in prophase (diplotene) of meiosis I and remain arrested until pub...