FINE STRUCTURE OF THE HUMAN OVUM IN THE PRONUCLEAR STAGE

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Abstract
A penetrated ovum was recovered from the oviduct of a 33 year old surgical patient who had had sexual intercourse 26 hr. before the operation. The ovum was In the pronuclear stage. The ooplasmic organelles were mainly represented by mitochondria, endoplasmic reticulum [ER] components, and Golgi elements. Small vesicles were found in the space between the 2 sheets of the pronuclear envelope. These vesicles appeared to be morphologically similar to the ER vesicles In the ooplasm and were considered to be involved in pronuclear development. Numerous annulate lamellae were seen in the ooplasm as well as in the pronuclei. Ooplasmic crystalloids were also observed. These were thought to represent cytoplasmic yolk. Remnants of the penetrating spermatozoon were found in close relation to one of the pronuclei. The fine structure of the 1st and 2nd polar body is also described. The nuclear complement of the 1st polar body consisted of isolated chromosomes, whereas the 2nd polar body contained a membrane-bounded nucleus. In consideration of the possibility that polar body fertilization may take place, these differences in nuclear organization could be of importance. Other recognizable differences between the 2 polar bodies were presence of dense cortical granules and microvilli in the 1st polar body, and absence of these structures in the 2nd. These dissimilarities were considered to be related to the organization of the egg cytoplasm at the time of polar body separation.