In mammals, sperm is generated in long, thread-like tubes, called seminiferous tubules (beige). Each tube is lined with an epithelium that contains spermatogonia cells (blue). Over the course of ~64 days, these cells differentiate into mature sperm cells (yellow). The spermatogonia cells divide by mitosis to produce diploid spermatocytes (lavender), which then undergo meiosis to generate two haploid spermatids. Spermatids develop further through “spermatogenesis” into the elongated spermatozoa (yellow).
Image: Cross section of a rat seminiferous tubule imaged with a Phillips 501 scanning electron micrograph (~500X). The spermatogonia and spermatocytes are colored blue and lavender, respectively, while the mature sperm cells are yellow. Color was added with the paintbrush in “Color” mode on Photoshop; the “plastic wrap” filter was then applied to add a glistening appearance.