Testis differentiation in the fetal and postnatal ferret.

Testis development has been examined in a series of 59 fetal and 9 postnatal ferrets from day 22 of the 40-42 day pregnancy, to 12 days after birth. Developing seminiferous tubules and interstitial cells were first seen on day 26, and were well established one day later. Differentiation was associated with cell enlargement and cell division, and consequently the testes grew distinctly more rapidly at this time than the corresponding ovaries. Up to the end of pregnancy the epithelioid interstitial cells, derived from stromal tissue, formed a large proportion of the testis. Lipid was distinguishable in them, histologically, from about day 30. As in various other mammals, there appeared to be some regression of the interstitial Leydig cells around the time of birth, when the seminiferous tubules resumed their growth. The intra-gonadal rete was present from day 22 onwards; it established connexions with the seminiferous tubules through the small tubuli recti by day 32.