. The chordates. Chordata. Reproduction 265 the blastodermic vesicle—very suggestive of an abortive blastopore. It is along the mammalian primitive streak, as in the similar sauropsidan structure, that rapid proliferation of cells produces a mesoderm (Fig. 221) which progressively interpolates itself between the already sepa- rated ectoderm and endoderm and spreads eventually into all regions of the embryo. The mesoderm is at first a continuous layer—unseg- mented—and devoid of Fig. 219. Early stage of the blasto- dermic vesicle of the hedgehog. (EC) Ectoderm; (EN) endoderm; (L) lacun
. The chordates. Chordata. Reproduction 265 the blastodermic vesicle—very suggestive of an abortive blastopore. It is along the mammalian primitive streak, as in the similar sauropsidan structure, that rapid proliferation of cells produces a mesoderm (Fig. 221) which progressively interpolates itself between the already sepa- rated ectoderm and endoderm and spreads eventually into all regions of the embryo. The mesoderm is at first a continuous layer—unseg- mented—and devoid of Fig. 219. Early stage of the blasto- dermic vesicle of the hedgehog. (EC) Ectoderm; (EN) endoderm; (L) lacunas, spaces occupied by maternal blood; (T) trophoblast (trophoderm). (After Hubrecht. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Rlakiston Company.). 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 Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : Blakiston
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