The origin of protein and fatty yolk in Rana pipiens. I. Phase microscopy.

Study of living frog oocytes with the phase microscope has shown that the early yolk appears in two forms. One of these, the protein yolk, consists of thin, dense, plate-like bodies which in face view are almost always regular hexagons. The other form, the fatty yolk, occurs as clusters of globules of varying sizes. The plate-like bodies occur both singly and in clusters. As the oocytes mature these plate-like bodies grow in size while retaining their hexagonal outline. Mitochondria have been observed to increase in length and numbers as the oocytes mature; they are rods or filaments at all stages of growth up to an oocyte diameter of 300 microns. The oocyte cytoplasm gradually becomes packed with long mitochondria, plate-like bodies, and clusters of globules.