The embryology of testicular descent.

A description is given of the role of the gubernaculum testis in the migration of the testis from the intra-abdominal to the scrotal position. The morphological differences in the process between carnivores, ungulates and man on the one hand and rodents on the other are stressed. The importance of gubernacular outgrowth, gubernacular regression as well as the importance of intra-abdominal pressure is emphasized. The effects of some forms of abnormal gubernacular development on testicular descent are described. The hormonal factors possibly involved in the regulation of the gubernacular reaction are evaluated. LH-RH, gonadotropins, AMH and testosterone seem not to be responsible for gubernacular outgrowth but a low molecular weight fraction of a fetal testicular extract, called descendin, is stimulatory to gubernacular cells. There are indications that testosterone plays a role in the initiation of gubernacular regression.