Anatomy of testis or testicle:

The testes are a paired organ in the scrotum. The testicular parenchyma is composed of between 250 and 350 lobules which drain to the mediastinum testis and then to the epididymis. These lobules are what make up the cells of this organ to store what are basically stem cells until they pass into the semen and wait 60-80 days to become spermatocytes capable of being used to reproduce the offspring when joined with a fertile female egg from the ovary.

The epididymis contains the semen that allows the sperm cells from the testis to develop into a spermatocyte.

Histology of the testis:

The seminiferous tubules contain the germinal epithelium. One or several seminiferous tubules which are highly convoluted form one lobule of the testis. The spermatogonia (plural for spermatogonium or single sperm cell) form the basal layer of the germinal epithelium. Spermatogonia are kind of like the stem cells of the spermatocytes until the spermatogonia  develop into the spermatocytes after a couple of months. There is a process called meiosis which allows for the development of these spermatogonia (stem cells) into spermatocytes.

Testes and Male Hormones:  

There are two basic functions of the testes. One is for the endocrine function of a testosterone inhibin and the other is for the exocrine function of spermatogenesis (creation of sperm cells). The Hypothalamic-Pituitary-Gonadal hormone axis is what controls each  function of the testes.