. The development of the chick; an introduction to embryology. Birds -- Embryology. prJ-^.^.. t^' fct'^mw^ ^ ' ^^-€sf^. % Mes. >J!S^ Fig. 38. — Transverse sections through a very short primitive streak of the chick. Incubated 17^ hours; no head-process. A. Through the anterior end of the primitive streak (primitive knot). Mesodermal cells are being proliferated from the ectodermal thickening; some are scattered between the two primary germ layers. The entoderm shows no proliferation, though some mesoderm cells are adhering to it. B. Fourteen sections posterior to A. (Entire length of the pr
. The development of the chick; an introduction to embryology. Birds -- Embryology. prJ-^.^.. t^' fct'^mw^ ^ ' ^^-€sf^. % Mes. >J!S^ Fig. 38. — Transverse sections through a very short primitive streak of the chick. Incubated 17^ hours; no head-process. A. Through the anterior end of the primitive streak (primitive knot). Mesodermal cells are being proliferated from the ectodermal thickening; some are scattered between the two primary germ layers. The entoderm shows no proliferation, though some mesoderm cells are adhering to it. B. Fourteen sections posterior to A. (Entire length of the primitive streak is 80 sections.) The mesoblast wings are forming; the primitive groove and primitive folds are indicated. The entoderm is free from the mesoderm. Ect. Ectoderm. Ent., Entoderm. Mes., Mesoderm, pr. f., Primitive fold. pr. gr. Primitive groove, pr. kn., Primitive knot. ning to spread out laterally. The entoderm is a continuous membrane without any connection with the primitive streak, and there are no cells between ectoderm and entoderm save those derived from the primitive streak. Figs. 38 A and B show the structure 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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