. The physiology of reproduction. Reproduction. 126 THE PHYSIOLOGY OF REPRODUCTION. the membrana granulosa lining the folhcle, and the discus proUgerus surrounding the ovum. The innermost cells of the discus rest upon a thick, transparent, radially striated membrane with a granular outer border. This is the zona radiata or zona pellucida. The striated appearance is due to the presence of fine canals. Within the zona, and immediately enclosing the ovum, another very thin membrane can sometimes be made out. This is the vitelhne membrane. The membrana granulosa and discus prohgerus are united by
. The physiology of reproduction. Reproduction. 126 THE PHYSIOLOGY OF REPRODUCTION. the membrana granulosa lining the folhcle, and the discus proUgerus surrounding the ovum. The innermost cells of the discus rest upon a thick, transparent, radially striated membrane with a granular outer border. This is the zona radiata or zona pellucida. The striated appearance is due to the presence of fine canals. Within the zona, and immediately enclosing the ovum, another very thin membrane can sometimes be made out. This is the vitelhne membrane. The membrana granulosa and discus prohgerus are united by one or more strands of f olhcular epithelial cells. A viscid fluid, containing protein matter, collects between them and becomes gradually increased in quantity .as the foUicle continues to grow.^ The liquor folliculi begins to form in the developing rat's ovary at about the ninth day of pregnancy.^ Miss Lane-Claypon suggests that the kary- olytic changes which occur in the nuclei of the follicular epithehal cells may have some connection with the origin of the Uquor. She states, how- ever, that in the process of formation of the Uquor follicuH in the adult ovary, the foUicle cells appear simply to disintegrate and dissolve without showing the phenomena of karyolysis. On the other hand Honore,^ who has investigated the subject in the case of the rabbit, concludes that the liquor folhouU is secreted by the foUicle cells, without their undergoing destruction (or that, if this occur, it is immaterial to the process of Uquor formation), in the same way as the urine is secreted by the epitheUum of the renal ' Occasionally a Graafian follicle may contain more than one ovum, but this is abnormal. Such follicles have been described as occurring in the rabbit's ovary by Honore ("Recherches sur I'Ovarie da Lapin," Arch, de Biol., vol. xvii. 1901), and in the dog's ovary by Smyth (" An Unusual Graafian Follicle," Biol. Bull., vol. xiv., 1908). The latter writer states
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