ULTRASTRUCTURAL CHANGES IN DEVELOPING CHICK LIVER .I. GENERAL CYTOLOGY

The cytological changes accompanying the differentiation of the liver of the chick have been investigated from its first appearance on the third day of incubation, through hatching, and up to the fifteenth day after hatching. The appearance of glycogen and lipid are discussed in the light of recent findings of [beta] granule formation in the pancreas and other available data. Activation of the Golgi complex takes place on the 4th to 5th day of incubation as judged by its expansion and the formation of a variety of vesicles. Mitochondria are sparse and have an average diameter of 0.2 [mu] at 4 days of incubation which increases to over 1 [mu] at hatching and then decreases to approximately 0.5 [mu]. The endoplasmic reticulum (ER) is very sparse at 3 days of incubation and appears first mainly in a vesicular form which eventually changes to a cisternal form and becomes closely associated with the plasma membrane and mitochondria, a single cisterna surrounding almost every mitochondrion. The rough ER gives rise to the smooth vesicular ER associated with glycogen deposition. Polyribosomal groups are frequently seen in the cytoplasm from the 8th day on. Microbodies become more numerous at hatching and are frequently located in the glycogen-lipid areas.