The yolk platelets of mature eggs and young embryonic cells of all amphibian species studied (Rana pipiens, Triturus pyrrhogaster, Diemictylus viridescens, Rana nigromaculata, and Bufo vulgaris) have a superficial layer of fine particles or fibrils (ca. 50 A in diameter), a central main body with a crystalline lattice structure, and an enclosing membrane approximately 70 A in thickness. Electron micrographs of the main body reveal hexagonal net (spacing ca. 70 A), square net (spacing ca. 80 A), and parallel band (spacing from 35 to 100 A but most frequent at ca. 70 A) patterns. The crystalline structure is believed to be a simple hexagonal lattice made of closely packed cylindrical rods. Each rod is estimated to be about 80 A in diameter and 160 A in length.