Prismatic Cristae and Matrix Granules in Mitochondria of the Kidneys of Ammocoetes

The kidneys of ammocoetes of Petromyzon marinas L . degenerate anteriorly and grow by the proliferation of the posterior nephrogenic tissue (1), which consists of small groups of cells surrounding narrow lumina. The cytoplasm of these cells contains large amounts of glycogen, smooth endoplasmic reticulum, lipid droplets, and mitochondria. This note describes prismatic cristae and granules within these mitochondria . Kidneys from ammocoetes of various ages were fixed for study with the electron microscope (2) . The proliferating tubules of the posterior tip were composed of differentiating cells undergoing mitosis which were unlike those found more anteriorly (3) . 1 Their mitochondria were of many shapes and sizes, but all contained angular cristae which appeared in transverse section as triangular prisms with sides measuring 400-450 A (Fig . I a) . Unlike the prismatic cristae of the anterior tubules,' these were arranged to form six-pointed "stars of David" (4), with their bases forming a hexagonal tube and their apices the points of the star (Fig . 1 a and b) . The tube had an inside diameter of 900 A and contained a single row of ovoid granules, each 300-350 A in diameter and as much as 1000 A long (Fig . 1, a-d) . The granules were connected by thin, electron-opaque strands (Fig . 1 c) . More thae six parallel prismatic cristae were often oriented so that the sides of a prism of one tube contributed to the formation of other hexagons, each surrounding its own row of granules (Figs. 1 c, 2) .