“…In fact it becomes clear in this study that it must be both, since the surface area of the organ increases with time. Many writers agree that sulcus formation begins near the middle of the organ and that there is a progressive increase in the number of lobes with the pas sage of time [von Ludwig, 1965;Meyer, 1969;Inke, 1974], The final number of lobes is the result of subdivision and not of fusion [Inke and Schindelheim, 1974;Fine and Keen, 1976], and although fusion of tis sues occurs on the surface of the kidney, obliterating sulci, the underlying units remain discrete and have not fused. The findings in this study are in accord with these observations.…”