Paired nerves from the brain and ganglia innervate the body. Long strands may have small terminal ganglia. The reproductive system is composed of a single saccular gonad in a coelomic pouch Iying dorsal to the digestive system. In the Eutardigrada, gonoducts open into the rectum. In Heterotardigrada, gonoducts open to the outside through a preanal gonopore.
Males possess two vas deferentia, a swollen portion serving as a seminal vesicle.
Females possess a single oviduct which passes to the right of the intestine. In accordance with the small size of tardigrades, there is no respiratory or circulatory system. For some species of tardigrades, no males have been found. Parthenogenesis occurs in two fashions. In diploid tardigrades, meiosis distributes chromo- somes hetween the oocyte and the polar body.