. The development of the chick; an introduction to embryology. Birds -- Embryology. 88 THE DEVELOPMENT OF THE CHICK is a layer of the mesoderm (Fig. 41). If the blood-islands be reckoned as mesoderm we must distinguish two layers of the latter, yiz., a deep or vascular layer (angioblast) lying next the germ-wall, and an upper layer next the ectoderm, which may be called the coelomic mesoderm, inasmuch as the body-cavity (coelome) develops within it later. pre prstr. d vase. Fig. 45. — Blastoderm and embryo at the stage of four- teen somites. The horns of mesoblast are on the point of meeting i
. The development of the chick; an introduction to embryology. Birds -- Embryology. 88 THE DEVELOPMENT OF THE CHICK is a layer of the mesoderm (Fig. 41). If the blood-islands be reckoned as mesoderm we must distinguish two layers of the latter, yiz., a deep or vascular layer (angioblast) lying next the germ-wall, and an upper layer next the ectoderm, which may be called the coelomic mesoderm, inasmuch as the body-cavity (coelome) develops within it later. pre prstr. d vase. Fig. 45. — Blastoderm and embryo at the stage of four- teen somites. The horns of mesoblast are on the point of meeting in front of the head. a. p., Area pelliicida. a. vase, Area vasculosa. a. v. Area vitellina interna. Ht., Heart, n. F., Neural folds. pr'a., Proamnion, pr. str., Primitive streak. S. t., Sinus terminalis. There are two sharply contrasted views concerning the origin of the mesoblast in the area opaca. According to the one point of view it is simply a peripheral extension of the primitive streak mesoblast with which as a matter of fact it is continuous (Hert- wig, Rabl, and others). AccorcUng to the other point of view. 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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