. The development of the chick; an introduction to embryology. Birds -- Embryology. Fig. 43. — Diagrams to illustrate the theory of concrescence as applied to the primitive streak of the bird. The central area bounded by the broken line represents the pellucid area; external to this is the area opaca, showing as concentric zones the germ-wall (G. W.), the zone of junction (Z. J.), and the margin of overgrowth (M. O.). m. n., Marginal notch. For de- scription see text. The most obvious interpretation of the head-process is as an outgrowth from the primitive knot. But another, and more prob
. The development of the chick; an introduction to embryology. Birds -- Embryology. Fig. 43. — Diagrams to illustrate the theory of concrescence as applied to the primitive streak of the bird. The central area bounded by the broken line represents the pellucid area; external to this is the area opaca, showing as concentric zones the germ-wall (G. W.), the zone of junction (Z. J.), and the margin of overgrowth (M. O.). m. n., Marginal notch. For de- scription see text. The most obvious interpretation of the head-process is as an outgrowth from the primitive knot. But another, and more proba])le interpretation in view of all the facts, is that the head- process is a later stage of the anterior end of the primitive streak;. 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 Lillie, Frank Rattray, 1870-1947. New York, Holt
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