FINE STRUCTURE OF HUMAN FOETAL TESTIS .1. INTERSTITIAL TISSUE

Thirteen male human foetuses ranging in crown-rump length from 29 to 212 mm (ages 8-27 weeks) were studied. Four developmental phases are distinguished. 1. The predifferentiation phase (below 8 weeks): The interstitium contains only undifferentiated mesenchymal cells. 2. The differentiation phase (8-14 weeks): Leydig cells develop and gradually fill the space between the germ cords. 3. The maturity phase (14-18 weeks): The interstitium occupies more than one half of the total area in the testis sections and is filled with mature foetal Leydig cells. 4. The involution phase (18-40 weeks): Most of the Leydig cells gradually degenerate and disappear. The foetal Leydig cells are packed with tubular agranular endoplasmic reticulum (AER). Islets of parallel granular ER membranes and other organelles are embedded in the AER. The mitochondria vary in shape and form, the cristae being mainly tubular. Some mitochondria like organelles contain electron dense inclusions. Dark membrane bound bodies of variable form and resembling the Golgi cisternae are present in most cells. Reinke crystals are never found in the foetal cells. In degenerating Leydig cells the AER appears in vesicular form, membranous whorls are seen in some of them and the cell membrane seems to rupture finally, and cytoplasmic material protrudes outside the cells. The fine structure of the mature foetal Leydig cells is suggested to reflect signs of human chorionic gonadotrophin stimulation. © 1969 Springer-Verlag.