. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. GASTRULATION IN VARIOUS CHORDATA 437 the blastoderm (fig. 211 A, B). This posterior prominence of the germ ring forms the embryonic shield. As gastrulation begins, the entodermal cells of the primary hypoblast at the caudal edge of the embryonic shield stream forward below the epiblast toward the anterior end of the blastodisc (figs. 210A, D). Coincident with this for- ward movement of the primary hypoblast, a small, crescent-shaped opening EMBRYO
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. GASTRULATION IN VARIOUS CHORDATA 437 the blastoderm (fig. 211 A, B). This posterior prominence of the germ ring forms the embryonic shield. As gastrulation begins, the entodermal cells of the primary hypoblast at the caudal edge of the embryonic shield stream forward below the epiblast toward the anterior end of the blastodisc (figs. 210A, D). Coincident with this for- ward movement of the primary hypoblast, a small, crescent-shaped opening EMBRYONIC SHIELD NEURAL PLATE MATERIAL ^, r-Ti'Ejej-'-E;::^.^ GERM RING. â E M B RVONI C Fig. 210. Gastrulation in teleost fishes. (A) Sagittal section of early gastrula. (Modi- fied slightly from Wilson, 1889.) (B) Midsagittal section through late teleost gastrula. The dorsal and ventral lips of the blastopore are shown approaching each other. (Modi- fied slightly from Wilson, 1889.) (C) Beginning gastrula of early blastoderm of brook trout, Salvelinus. Observe inward (forward) migration of primary hypoblast cells and thickened mass of cells which arises at posterior margin. (After Sumner, '03.) (D) Later stage in gastrulation of brook trout. (After Sumner, '03.) (E) Transverse section of late gastrula of brook trout, showing the three germ layers. (After Sumner, '03.) (F) Transverse section through late gastrula of sea bass. (After Wilson, 1889.) (G) Midsagittal section through closing blastopore of sea bass. (After Wilson, 1889.) (H) Longitudinal section through late gastrula of the brook trout. (After Sumner, '03.). 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 Nelsen, Olin E. (Olin Everett), b. 1898. New York, Blakiston
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