. The development of the chick; an introduction to embryology . ). The development of the embryo (hiring thesame period is inchoated in the same Fig. 32. — A. Hens egg at about the twenty-sixth hour of incubation, toshow the zones of the lilastoderni antl tlie orientation of the embryo withreference to the axis of the shell. (After Duval.)B. Yolk of hens egg incubated about 50 hours to show the extent ofovergrowth of the blastoderm. (After Duval.) A. C, Air chamber, a. \>., Area pellucida. a. v., Area vasculosa. a. v. e.,Area vitellina externa, a. v. L, Area vitellina interna. Y.,
. The development of the chick; an introduction to embryology . ). The development of the embryo (hiring thesame period is inchoated in the same Fig. 32. — A. Hens egg at about the twenty-sixth hour of incubation, toshow the zones of the lilastoderni antl tlie orientation of the embryo withreference to the axis of the shell. (After Duval.)B. Yolk of hens egg incubated about 50 hours to show the extent ofovergrowth of the blastoderm. (After Duval.) A. C, Air chamber, a. \>., Area pellucida. a. v., Area vasculosa. a. v. e.,Area vitellina externa, a. v. L, Area vitellina interna. Y., Uncoveredportion of yolk. The blastoderm eaiIy becomes divided in two hiyers as faras the margin of the vascular area. The outer layer, knownas the somatopleure, is continuous with the body-wall, which isopen ventrally in the young embryo. The inner one, known astlie splanchnoj)leure, is continuous with the wall of the intestinewhich is likewise open ventrally. The space between these twomembranes, the extra-em]:)ryonic body-cavity, is continuouswith the body-cavity of the embryo, lltimately, the splittingof the blastoderm is carried around the
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