Microscopic Appearance of the Testes The testes are the primary male sex organs. The testes are housed outside of the pelvic cavity in the scrotum. Let's examine the microscopic appearance of the testes. Once mature, the testes produce sperm and testosterone. These two major functions of the testes are carried out in two separate locations. The seminiferous tubules, seen here in cross section, are where sperm cells are produced. Interstitial cells are found in between the seminiferous tubules. Interstitial cells produce the hormone testosterone. This is a cross section through one seminiferous tubule at a higher magnification. Notice that it's hollow. Sperm production occurs in a seminiferous tubule by a process called spermatogenesis. As sperm are produced, they move from the outer periphery of the seminiferous tubule toward the lumen. Notice the threadlike flagella of the developing sperm cells in the lumen of the seminiferous tubule. Let's look at the two categories of cells that make up the wall of a seminiferous tubule. These are sustentacular cells, which form the structural foundation of the tubule wall. Sustentacular cells form a continuous border around the wall of the tubule, although this can't be easily seen using a microscope. Notice their elongated nuclei with prominent nucleoli. Sustentacular cells do not transform into sperm cells. The other cells that make up the seminiferous tubule are spermatogenic cells, which form sperm cells. Spermatogenic cells have specific names based on the stage of miosis they are in. Spermatogonia are undifferentiated cells that have not entered miosis. They are found hugging the basement membrane of a seminiferous tubule. Once a spermatogonium begins the process of miosis, it's known as a primary spermatocyte, even though it hasn't divided yet. Primary spermatocytes can be identified by their large clumps of chromosomes. Secondary spermatocytes result from the first miotic division of the primary spermatocyte and can be hard to distinguish visually. Secondary spermatocytes give rise to spermatids, which can be identified by their smooth nuclei. Spermatids transform into sperm cells, also known as spermatozoa, through a process called spermatogenesis. Let's finish by reviewing the microscopic appearance of the testes. Interstitial cells. Seminiferous tubules. Sustentacular cells. Spermatagonia. Primary spermatocytes. Spermatids. Flagella.