Solution

In testis, the immature male germ cells (spermatogonia) produce sperms by spermatogenesis, that begins at puberty. The spermatogonia (singular spermatogonium) present on the inside wall of seminiferous tubules, multiply by mitotic division and increase in numbers. Each spermatogonium is called as primary spermatocytes periodically undergo first meiotic division (reduction division) and produces two equal, haploid cells, called secondary spermatocytes, which have only 23 chromosomes each. The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids. The spermatids are then transformed into spermatozoa (sperms) by the process called spermiogenesis. After spermiogenesis, mature sperms are finally released from the seminiferous tubules by the process called as spermiation. Thus, the correct answer is option D.