The oocyte of the domestic chicken shortly after hatching, studied by electron microscopy

ABSTRACT Oocytes taken from chickens from 1 day to 11 weeks after hatching have been examined by electron microscopy. Early extra-follicular oocytes have chromosome filaments in the nucleus at the prophase of meiosis. The fine structure of these filaments is described and is found to vary according to the size and age of the oocyte. The Balbiani body present in oocytes of about 8-20 μ in diameter has been shown to consist of paired centrioles surrounded by Golgi vesicles and an outer border of mitochondria. Golgi vesicles and mitochondria were dispersed in larger oocytes, and in those larger than about 80 μ the mitochondria formed a cortical layer. In oocytes with a diameter greater than about 100 μ macrobodies (clusters of lining bodies) were mainly confined to the periphery of the oocyte, whereas in others they were present, together with lipid drops, mainly in the interior. Folding of the oocyte membrane was observed in many oocytes measuring about 100 μ in diameter, but was much more pronounced in oocytes above 250 μ. In these oocytes cortical vesicles in close proximity to the crypts of the folds appear to have been formed by pinocytosis. In the follicle cells of oocytes 250 in diameter and over, large masses of glycogen granules occur in the cytoplasm near the oocyte membrane.