. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. TYPES OF CHORDATE BLASTULAE 367 EPI BLAST ENTODERM OR PRIMARY HYPOBLAST. NEURAL ECTODERM NOTOCHORD ENTODERM DORSAL 8LAST0P0RAL LIP Fig. 180. Presumptive organ-forming areas of the teleost fish blastoderm. (A) Median section through the late blastoderm of Fundidus heteroclitus just previous to gastrulation. Somewhat schematized from the author's sections. Presumptive entoderm or hypoblast is shown exposed to the surface at the caudal end of the bla
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. TYPES OF CHORDATE BLASTULAE 367 EPI BLAST ENTODERM OR PRIMARY HYPOBLAST. NEURAL ECTODERM NOTOCHORD ENTODERM DORSAL 8LAST0P0RAL LIP Fig. 180. Presumptive organ-forming areas of the teleost fish blastoderm. (A) Median section through the late blastoderm of Fundidus heteroclitus just previous to gastrulation. Somewhat schematized from the author's sections. Presumptive entoderm or hypoblast is shown exposed to the surface at the caudal end of the blastoderm and, therefore, follows the conditions shown in (B). (B) Presumptive organ-forming areas of the blastoderm of Fiindulus heteroclitus. Arrows show the direction of cell move- ments during gastrulation. (Modified from diagram by Oppenheimer, '36.) appears. Within the inner cell mass, two types of cells are present, namely, formative and trophoblast (figs. 177B; 178A). (2) Unlike that of the marsupial mammal, an overlying layer of tropho- blast cells, covering the layer of formative cells, always is present (fig. 177B). In some cases (rabbit, pig, and cat) they degenerate (the cells of Rauber, fig. 177C), while in others (man, rat, and monkey) the overlying cells remain and increase in number (fig. 178A-E). (3) The entodermal cells arise by a separation (delamination) of cells from the lower aspect of the inner cell mass (figs. 177C; 178A), with the exception of the armadillo where their origin is similar to that of marsupials. With these differences, the same essential goal arrived at in the marsupial mammals is achieved, namely, a bilaminar, formative area, the embryonic disc, composed of epiblast and hypo- blast layers (figs. 177D; 178D, E), which ultimately gives origin to the embryonic body. A bilaminar, extra-embryonic, trophoblast area, consisting of extra-embryonic entoderm and ectoderm, also is formed (figs. 177D; 178D, E). The secondary blastocoel originates betw
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