. Embryology. Embryology; Embryology; genealogy. Fig. 164. The relation of the grow- ing chick embryo to its source of nutri- ments. During very early development the blastoderm is in direct contact with the yolk and the products of digestion diffuse into the cells. With a larger mass of cells, as in the embryo, blood vessels develop which convey the digested prod- ucts to the embryo. Finally in the later stages of development the yolk is en- closed in a sac composed of endoderm and mesoderm. The endoderm digests the yolk and the blood vessels transport sub- stances to the growing chick. ARTER
. Embryology. Embryology; Embryology; genealogy. Fig. 164. The relation of the grow- ing chick embryo to its source of nutri- ments. During very early development the blastoderm is in direct contact with the yolk and the products of digestion diffuse into the cells. With a larger mass of cells, as in the embryo, blood vessels develop which convey the digested prod- ucts to the embryo. Finally in the later stages of development the yolk is en- closed in a sac composed of endoderm and mesoderm. The endoderm digests the yolk and the blood vessels transport sub- stances to the growing chick. ARTERIES. can be used by the growing cells (Fig. 164). As the embryo gets larger, how- ever, the endoderm incorporates this yolk into a sac—the yolk sac. The blood vessels—the vitelline veins and arteries—then serve to transport the materials from the yolk to the embryo. The circulation carries substances to the growing parts of the chick embryo, where they are utilized for the synthesis of new proteins. The yolk sac, therefore, is the embryonic digestive system. In the yolk-sac membrane the enzymes break up the yolk into diffusible products, which go through the blood vessels to the heart and thence to the rest of the embryo. The yolk thus provides the raw materials for growth—proteins, fats, and to some extent, carbohydrates. The composition of the yolk is discussed in Chapter 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 Barth, Lester G. (Lester George), 1905-1979. New York, Dryden Press
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