Henry Gray (1825–1861). Anatomy of the Human Body. 1918.
Human ovum examined fresh in the liquor folliculi. (Waldeyer.) The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmic area and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot.