Light and electron microscopy on the proximal convoluted tubules during the postnatal development.

It has been established in the mammalian kidneys during the postnatal development that the primordial tubules, blastema, are piled up beneath the renal capsula, elongating themselves in order to be conjugated with the tips of the collecting tubules which had been already accomplished in embryonic life (K it t el son 1917 A r a t a k i 1926 ; Baxter and Y o f f e y 1948). The proximal convoluted tubules in embryonic and infantile growing kidneys are provided with the simple and uncluttered ultrastructure, which is considered useful to understand the complicated ultrastructure in the adult. There have been so far a few reports about this subject., Clark (1957) described the differentiation of tubular cells in newborn mice by electron microscope. Suzuki (1958) carried out the electron microscopy on the differentiation of the cells of proximal convoluted tubule in embryonic, newborn and adult rats. Leeson (1959, 1960) made the electron microscopy on the development of mesonephros and metanephros in rabbits. On the other hand, investigatons on the ultrastructure concerning the the proximal convoluted tubules of the adult mammals have been accumulated (S j o strand and R ho din 1953 ; P o 1 icard, 1954; Rhodin 1954, 1958a,b; Pease 1955; Weiss 1955; Rollhauser and Vogell 1957; Rollhauser 1957; Elias 1957; Montgomery and Breeman 1958; Miller 1960; Schmidt 1960). Above all, the diagrammatic representation by R ho din (1958a, b) has been highly appreciated. But it seems dif-