In the mole, Talpa europaea, there occurs a sequence of interstitial events comparable with that of seasonal birds, reptiles, and some fishes. There is a periodic accumulation and discharge of cholesterol and lipids in the Leydig cytoplasm. This cycle differs from its avian counterpart in that whereas in birds (and some fishes) the Leydig cells rapidly discharge their sudanophil contents before mating, the interstitium of the mole becomes exhausted much more slowly. Another difference is that the Leydig cells of the mole do not appear to become exhausted and replaced en masse as in birds after spermatogenesis. The seasonal growth and regression of the mammalian accessory sexual organs can be correlated with the increase and decrease of secretory activity of the interstitial cells (as shown by their lipid cycle). In the seminiferous tubules of the mole there is no lipid cycle corresponding to that observed in sub-mammalian vertebrates.

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