The Fine Structure of the Hen’s Ovum at Ovulation

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Abstract
The cortical organization of the hen’s ovum at ovulation was examined. A fibrous reticulum, the perivitelline layer (PL), uniformly surrounded the ovum and was separated from the vitellus at the animal pole by the perivitelline space. This space may be completely occluded by yellow yolk in other regions of the ovum. The animal pole consisted of the nucleus of Pander and the blastodisc. These regions were characterized by the presence of clear vacuoles, white yolk spheres, mitochondria and glycogen granules all of which were absent from the remaining ovum. The pitted surface of the blastodisc was covered with microvilli and blunt-projections. Occasional pinocytotic pits were seen at their bases. The cortical cytoplasm of the blastodisc contained clusters of coated and uncoated dense vesicles and tubular profiles. Multiple fusion of these structures resulted in the formation of the clear vacuoles. The latter appeared to serve as compartments for the assimilation of yolk and subsequently developed into white yolk spheres.