Conclusion and Summary

Abstract

The mesonephroi of cat and sheep are morphologically highly differentiated organs with an ample enzyme pattern, which attain their functional maturity before most of the other organs systems of the embryo. Their function was proved by excretion experiments between the 26th and 40th day in the cat; the morphological and histochemical signs of maturity indicate a gradual onset of function at about the 18th day and an end on the 40th—42nd day. The functional period thus amounts to one third of the gestational period. In the sheep, it is to put between the 17th and the 55th day and amounts to 1/4 of the gestational period. Maturation processes can be observed up to the 32nd day in the mesonephros of the cat. In the sheep, there is a very quick maturation of the glomeruli, of the endocytic apparatus in the proximal tubular epithelia, and of the basal labyrinth. Together with other criteria like nephron length and vascularization, this early maturation indicates, that the mesonephros of the sheep is endowed with a greater functional capacity than that of the cat. For the mesonephroi of both species, the order of developmental complexity given by Bremer (1916) and Gersh (1937) can be confirmed in the declining range: pig, sheep, cat, rabbit, guinea pig, man, and rat.