The male's reproductive system contains a pair of testes, usually located near the back of the abdomen. Each testis is subdivided into functional units (called follicles) where sperm are actually produced. A typical testis may contain hundreds of follicles, generally aligned parallel to one another. Near the distal end of each follicle, there are a group of germ cells (spermatogonia) that divide by mitosis and increase in size to form spermatocytes. These spermatocytes migrate toward the basal end of the follicle, pushed along by continued cell division of the spermatogonia. Each spermatocyte undergoes meiosis: this yields four haploid spermatids which develop into mature spermatozoa as they progress further along through the follicle.
Mature sperm pass out of the testes through short ducts (vasa efferentia) and collect in storage chambers (seminal vesicles) that are usually little more than enlarged sections of the vasa. Similar ducts (vasa deferentia) lead away from the seminal vesicles, join one another near the midline of the body, and form a single ejaculatory duct that leads out of the body through the male's copulatory organ (called an aedeagus).
One or more pairs of accessory glands are usually associated with the male's reproductive system. These are secretory organs that connect to the reproductive system by means of short ducts -- some may attach near the testes or seminal vesicles, others may be associated with the ejaculatory duct. The glands have two major functions:
- Manufacture of seminal fluid, a liquid medium that sustains and nourishes mature sperm while they are in the male's genital system.
- Production of spermatophores, pouch-like structures (mostly protein) that encase the sperm and protect them as they are delivered to the female's body during copulation.