. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. ^Tnfl Fig. 62. — Embrvo of Amphioxus at the stage at which it ruptures the follicle and becomes free-swimming. A. Seen from above as a semi-opaque object. (After KOWALEVSKY.) B. Seen in sagittal (optical) section. (After Hatschek.) arc. Archenteron. Medullary plate. Myoccelomic pouches of archenteron. Posterior neurenteric canal. the possession of a ciliated ectoderm is very common among Invertebrate embryos, but entirely unknown among the craniate Vertebrates. The medullary plate
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. ^Tnfl Fig. 62. — Embrvo of Amphioxus at the stage at which it ruptures the follicle and becomes free-swimming. A. Seen from above as a semi-opaque object. (After KOWALEVSKY.) B. Seen in sagittal (optical) section. (After Hatschek.) arc. Archenteron. Medullary plate. Myoccelomic pouches of archenteron. Posterior neurenteric canal. the possession of a ciliated ectoderm is very common among Invertebrate embryos, but entirely unknown among the craniate Vertebrates. The medullary plate is now being closed off from the outer surface. This is effected by the co-operation of two factors. The ectoderm which bounds the medullary plate laterally, grows over it, and simultaneously the ectoderm of the posterior or ventral lip of the blastopore grows for- ward over the medullary plate so as to shut in the blasto- pore from the exterior (Fig. 62 A and B). The archenteric. 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 Willey, Arthur, 1867-. New York, London, Macmillan
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
