. The development of the chick; an introduction to embryology . f to this author they are derived, like the primitive ova, fromthe germinal epithelium, in which he agrees with the majority of hispredecessors. He states that the period of multipli( atioii of the ovo-gonia ends about the time of hatching; that the period of growth of theovocytes begins at about the fourteenth day of incubation (seven daysbefore hatching), and before the formation of the primordial follicle,which begins on the fourth day after hatching. Thus the periods ofmultiplication and growth overlap. He
. The development of the chick; an introduction to embryology . f to this author they are derived, like the primitive ova, fromthe germinal epithelium, in which he agrees with the majority of hispredecessors. He states that the period of multipli( atioii of the ovo-gonia ends about the time of hatching; that the period of growth of theovocytes begins at about the fourteenth day of incubation (seven daysbefore hatching), and before the formation of the primordial follicle,which begins on the fourth day after hatching. Thus the periods ofmultiplication and growth overlap. He gives a detailed and well-illus-trated account of the nuclear changes accompanying the first stages ofgrowth (synapsis, etc.) 28 THE DEVELOPMENT OF THE CHICK Altliouf2;h the imculeus (germinal vesicle of authors) maybe excentric in position in the youngest ovocytes, it alwaysoccupies an approximately central position in those slightlyolder. The nucleus increases in size with the growth of thecell-bodv; in the voungest ovocvtes its diameter is about 9 /a. and. Fig. 7. — Section of an ovarian ovum of the pigeon; drawn from a prepara-tion of Mr. J. T. Patterson. The actual dimensions of the ovum are s., Stalk of follicle. (!. V., (lerminal vesicle. Granulosa. L., Latebra. ]). P., Peripheral protoplasm, pr. f., Primordial follicles. Th. ex., Theca externa. Th. int., Thcca interna. Y. Y., Yellow yolk. Z. r., Zona radiata. in the ri]ie ovmn it is flattened and measiu*es about 117x315 /A. It retains its central position until the ovtnn is about0.()() mm. in diameter, and then moves to the surface whereit lies almost in contact with the vitelline membrane (). It l)ecomes ellipticnl, and later tlie outer siu-face is flat- THE EGG 29 tenetl against the vitelline mem]:)rane, the inner surface re-maining convex (Fig. S). The point on the surface to whichthe germinal vesicle migrates is situated away from the surfaceof the ovary, and thus in the position
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