. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. FORMATION OF THE GERM LAYERS 49 forms an invagination (Fig. 25, gc), the roof of which is composed of relatively small yolk-containing cells while its floor is formed by the large cells of the lower pole of the blastula. The cavity of the blastula is not sufficiently large to allow of the typical invagination of all these large cells, so that they become enclosed by the rapid growth of the ectoderm cells of the upper pole of the ovum over. Fig. 25.—Section through a Gastrula of Amblystoma. dl
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. FORMATION OF THE GERM LAYERS 49 forms an invagination (Fig. 25, gc), the roof of which is composed of relatively small yolk-containing cells while its floor is formed by the large cells of the lower pole of the blastula. The cavity of the blastula is not sufficiently large to allow of the typical invagination of all these large cells, so that they become enclosed by the rapid growth of the ectoderm cells of the upper pole of the ovum over. Fig. 25.—Section through a Gastrula of Amblystoma. dl, Dorsal lip of blastopore; gc, digestive cavity; gr, area of mesoderm formation; mes, mesoderm.—(Eycleshymer.) them. Before this growth takes place the blastopore corresponds to the entire area occupied by the large yolk cells, but later, as the growth of the smaller cells gradually encloses the larger ones, it becomes smaller and is finally represented by a small opening situated at what will be the hind end of the embryo. Soon after the archenteron has been formed a solid plate of cells, eventually splitting into two layers, arises from its roof on each side of the median line and grows out into the space between the ecto- derm and endoderm (Fig. 26, mkl and mk2),.evidently corresponding to the hollow plates formed in the same situations in Amphioxus. 4. 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 McMurrich, J. Playfair (James Playfair), 1859-1939. Philadelphia : P. Blakiston's son & co.
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Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectembryology
