. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. EMBRYONIC DISC ^^^^^^P-^^^^^. Fig. 145. Early development of the pig. (A-E) Fate of the first two blastomeres. The larger blastomere of the two-cell stage gives rise to trophoblast tissue, whereas from the smaller blastomere, formative cells and trophoblast cells arise. (After Heuser and Streeter, Carnegie Inst., Washington, Contrib. Embryol., 20:3.) (F) Section of two- cell stage. Specimen secured from oviduct of sow, killed two days, 3'/2 hours
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. EMBRYONIC DISC ^^^^^^P-^^^^^. Fig. 145. Early development of the pig. (A-E) Fate of the first two blastomeres. The larger blastomere of the two-cell stage gives rise to trophoblast tissue, whereas from the smaller blastomere, formative cells and trophoblast cells arise. (After Heuser and Streeter, Carnegie Inst., Washington, Contrib. Embryol., 20:3.) (F) Section of two- cell stage. Specimen secured from oviduct of sow, killed two days, 3'/2 hours after ovula- tion. (G) Section of four-cell stage. Age is approximately IVi days. (H) Sixteen-cell stage, drawn from unsectioned specimen, probably 3'/2 days old. (I) Blastular stage. Specimen secured from sow, 4% days after copulation. (J-L) Stages showing the for- mation of the blastocoel. (J) About 4^/4 days after copulation. (K) Six days, 1% hours after copulation. (L) Six days, 20 hours after copulation. (M) Beginning dis- integration of trophoblast cells over the inner cell mass and separation of entoderm cells from the inner cell mass. (N) Trophoblast cells over inner cell mass almost absent, entoderm forms a definite layer below inner cell mass. (O) Trophoblast cells almost absent over the embryonic disc; entoderm layer continuous. (P-R) Stages shown in (M), (N), (O) respectively, showing the whole blastocyst. In (Q) the entoderm cells are shown migrating outward to line the cavity of the blastocyst. 298. 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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