. The elements of Embryology. Embryology. I.] THE OVARIAN OVUM. 13 The rest of the ovum is known as the yolk. This consists of two elements, the white yolk- and the yellow yolk-spheres, which are distributed respectively very much in the same way as in the laid egg, the yellow yolk forming the main mass of the ovum, and the white yolk being gathered underneath and around the disc (Fig. t, w. y), and also forming a flask-shaped mass in the interior. The delicate membrane surrounding tlie whole is the vitelline membrane. The youngest ova in the ovary of a fowl, in common with those of all other
. The elements of Embryology. Embryology. I.] THE OVARIAN OVUM. 13 The rest of the ovum is known as the yolk. This consists of two elements, the white yolk- and the yellow yolk-spheres, which are distributed respectively very much in the same way as in the laid egg, the yellow yolk forming the main mass of the ovum, and the white yolk being gathered underneath and around the disc (Fig. t, w. y), and also forming a flask-shaped mass in the interior. The delicate membrane surrounding tlie whole is the vitelline membrane. The youngest ova in the ovary of a fowl, in common with those of all other animals, present the characters of a simple cell. Such a cell is diagrammatically repre- sented in Fig. 5. It is seen to consist of a naked protoplasmic body containing in its interior a nucleus—the germinal vesi- cle—which in its turn envelopes a nucleolus—constituting what is known as the germinal spot. Such young ova are enclosed in a capsule of epithelium, named the follicle or follicular mem- brane, and are irregularly scat- tered in the stroma of the ovary. The difference between such an innnature ovum and the ripe ovum just described is very great, but throughout its growth the ovum retains the characters of a cell, so that the mature ova- rian ovum, equally with the youngest ovum in the ovary, is a single cell. The most striking changes which takes place in the Fig. Diagram ok the Ovum. (From Gegen- baur.) a. Granular proto- plasm, b. Nucleus (ger- miual vesicle), c. Nu- cleolus (germinal spot).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Foster, M. (Michael), Sir, 1836-1907. London, MacMillan
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