. Chordate anatomy. Chordata; Anatomy, Comparative. S -. Fig. 48.—Early stage of the Fig. 49.—Embryonic area or "shield" of the blastodermic vesicle of the hedge- blastodermic , vesicle of the rabbit after about hog. EC, ectoderm; EN, endo- 172 hours development. PS, primitive streak- derm; L, lacunae, spaces occupied 5-5. position of section represented in Fig. 50. by maternal blood; T, trophoblast (After Assheton.) (trophoderm). (After Hubrecht.) ther history of the two layers identifies them as embryonic ectoderm and endoderm. However, both in mode of origin and in further history
. Chordate anatomy. Chordata; Anatomy, Comparative. S -. Fig. 48.—Early stage of the Fig. 49.—Embryonic area or "shield" of the blastodermic vesicle of the hedge- blastodermic , vesicle of the rabbit after about hog. EC, ectoderm; EN, endo- 172 hours development. PS, primitive streak- derm; L, lacunae, spaces occupied 5-5. position of section represented in Fig. 50. by maternal blood; T, trophoblast (After Assheton.) (trophoderm). (After Hubrecht.) ther history of the two layers identifies them as embryonic ectoderm and endoderm. However, both in mode of origin and in further history the mammalian embryo at this stage shows perplexing discrepancies as com- pared to the gastrula of a lower vertebrate. As stated above, the material which constitutes the definitive embryo is within the thick and solid cell-mass (Fig. 47, /) of the early blastodermic vesicle. As development proceeds the behavior of this cell-mass is very much like that of the blastoderm of the embryo of a reptile or bird. If the cavity of the vesicle were occupied by yolk instead of b>- a watery fiuid the whole embryonic complex would resemble closely an early reptilian embryo. The thick cell-mass, lying in relation to the vesicular cavity much as the reptilian blastoderm lies upon the surface of the yolk, flattens and thins out to form the embryonic shield (Fig. 4q) in the axis of which appears an elongated thickening similar to 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 Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : P. Blakiston's Son & Co.
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Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
