Descent of Testis in Relation to Temperature

The Undescended Testis

“…It is common clinical and operative experience that the superficial inguinal ectopic testis approximates more nearly to the normal as regards size and consistency than the testis that is emergent or that lies in the inguinal canal or higher, and Mack, Scott, Ferguson-Smith, and Lennox (1961) found that while germ cell defects appeared histologically in both types, they were more marked in the true undescended organ than in the ectopic one. This observation may be related to the smaller temperature differential involved in the latter case; Badenoch (1945) found the difference between the scrotum and the inguinal region to average 0 *8 C.…”

“…Badenoch (1945) found the average difference between the intra-abdominal and intrascrotal temperatures in man to be 2. 20 C. In animal experiments, Moore (1924), Moore and Quick (1924), and Moore and Oslund (1924) noted the occurrence of degenerative changes in a testis that was replaced within the abdomen or, alternatively, was warmed by the application of external heat, and found also that the changes could be reversed when thermal normality was restored.…”

“…Not infrequently the vas and its accompanying artery extend to the fundus of the hernial sac and then loop back to the incompletely descended epididymis. On occasion the abnormalities are more gross: Badenoch (1946) recorded 3 cases of testicular undescent in which the epididymis was malformed and the vasa efferentia absent on histological scrutiny, and Devens (1964) described 2 cases where the vas deferens was atretic proximal to the epididymis. Such interruptions of ductal continuity may readily remain undetected at orchidopexy; it is likely that they are more common than would appear from the numbers recorded, and they may contribute significantly to the incidence of infertility associated with testicular retention.…”

“…It is inconceivable that a vulnerable external position confers any advantage as regards individual or species survival. Badenoch (1945) saw an analogy with the migration of certain fishes and birds to cooler climes for breeding and thought that the testes descend in search of a lower temperature. It seems more reasonable, however, to regard the thermal influence on the testis as an adaptation to, rather than the cause of its descent; in some mammals, for example the elephant and the whale, the testes remain permanently inside the abdomen without loss of fertility.…”

Studies on the fetal development of the gubernaculum in cetacea

“…There has developed a general agreement that homeothermia has been the key factor underlying male mammalian gonadal/genital migration to the extra-abdominal site (Moore, 1924;Badenoch, 1945;Cowles, 1965;Waites, 1970;Bedford, 1978;Afzelius, 1979;Frankenhuis and Wensing, 1979). With exceptions such as a tropical rodent (cane mouse: Bronson and Heideman, 1993) and rodents with incomplete cremaster sac development (Bedford et al, 1982), the usual body core temperature of around 37°C is lethal to sper-matogenesis (VandeMark and Free, 1970;Waites, 1970).…”