Nematode digestive systems are made of a tube of a single layer of cells - the intestine . Food enters the intestine from the esophagus, nutrients are absorbed, and wastes are released through the anus . The ovary is where germ cells give rise to eggs . Fertilization, by the sperm, takes place in the uterus and eggs are released through the vagina . Even though the size of nematodes varies greatly, most nematode eggs are about the same size and shape.
Most nematode species produce males and females, but some species only produce females.
Male nematodes produce sperm in the testes which are shaped similar to the female ovary. Sperm accumulate in the seminal vesicle and exit through the anus. During mating rigid spicules insert into the vagina and form a passageway for the sperm. Some males have thin cuticle extensions on both sides of the anus called bursae . A few species produce male and female structures within the same individual.