Spermatogenesis (formation of sperms)

Occurs in the walls of the seminiferous tubules. It has four phases:

1. Multiplication phase: the primary germ cells (2N) divide by mitosis many times, producing many spermatogonia (2N).
2. Growth phase: spermatogonia store food and grow in size, becoming primary spermatocytes (2N).
3. Maturation phase: each primary spermatocyte undergoes meiosis I → two secondary spermatocytes (N) → meiosis II → four spermatids (N) (the number of chromosomes is halved: 46 → 23).
4. Metamorphosis (differentiation) phase: the spermatids change into sperms — loss of most of the cytoplasm, formation of acrosome, tail, and mitochondria in the midpiece.

Result: one primary spermatocyte → 4 sperms, all functional. Spermatogenesis starts at puberty and continues throughout life, taking about 2–3 months.