Hímivarsejtet

Hímivarsejtet refers to the male reproductive tract in birds. It is comprised of a pair of testes and a pair of vasa deferentia. The testes are the primary sex organs responsible for producing sperm and male hormones, primarily testosterone. In most bird species, the testes are located within the body cavity, suspended from the abdominal wall by a fold of peritoneum called the mesorchium. Their size can vary significantly depending on the season, being much larger during the breeding season when sperm production is at its peak.

The vasa deferentia are ducts that transport sperm from the testes to the cloaca, the common exit point for the digestive, urinary, and reproductive systems. These ducts are typically narrow and coiled. In many bird species, the vasa deferentia widen near the cloaca to form seminal vesicles, which can store sperm temporarily. Unlike mammals, most male birds do not possess an external penis. Instead, reproduction usually involves a "cloacal kiss," where the cloacas of the male and female are brought into contact to transfer sperm. Some exceptions exist, such as in ducks and geese, which have a phallus that is everted during mating. The development and function of the hímivarsejtet are regulated by hormones, including gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH), in addition to testosterone.