The process of formation of sperms is called spermatogenesis. It occurs in the male gonads testes. Testes are made up of many semi niferous tubules lined by germinal epithelium. Cells of this layer divide to form spermatozoa in the following four steps:
(i) Multiplication Phase : At sexual matu rity, the undifferentiated primordial germ cells divide several times by mitosis to produce a large number of spermatogonia. These under go mitosis to form supermatogonia which move forwards the lumen of seminiferous tubules and enter growth phase. These cells are called spermatocytes.
(ii) Growth Phase Each type B sperma togonium actively grows to a larger primary spermatocyte by obtaining nourishment from the nursing cells. They are now called primary spermatocytes.
(ii) Maturation Phase : Each primary spermatocyte undergoes two successive divisions, called maturation divisions. The first maturation division is reductional or meiotic. Hence, the primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Both secondary spermatocytes now undergo second matura tion division which is an ordinary mitotic division to form, four haploid spermatids, by each primary spermatocyte.
(iv) Spermiogenesis : It is the process of transformation of circular spermatid to a spermatozoan. The spermatozoa are later on known as sperms. Thus, four sperms are formed from one spermatogonium. In this process the nucleus of the spermatid becomes the head of the sperm, it shrinks with closely packed DNA the golgi apparatus, containing proteolytic enzymes, becomes the acrosome cap. Axial filaments are formed from distal centriole and from the mitochondria, mitochondrial spiral is formed. Also the loss of cytoplasm takes place and only a sheath remains around mitochondria.
