. An elementary course of practical zoology. Zoology. XII DEVELOPMENT 201 small circular space—the blastopore, filled by a mass of yolk- cells—ih.^yolk-plug, is left uncovered (Fig. 64, G, Yi., ). Development of ttie Chief Organs.—In the meantime a second cavity appears in the interior of the embryo, and as it increases in size, the segmentation cavity undergoes a proportional diminution and finally disappears. This new Tnes. ent Fig. 65.—Transverse section through a frog-embryo during the formation oi the medullary canal. c. coslome ; ect. ectoderm ; end. endoderm ; ent. enteron ;
. An elementary course of practical zoology. Zoology. XII DEVELOPMENT 201 small circular space—the blastopore, filled by a mass of yolk- cells—ih.^yolk-plug, is left uncovered (Fig. 64, G, Yi., ). Development of ttie Chief Organs.—In the meantime a second cavity appears in the interior of the embryo, and as it increases in size, the segmentation cavity undergoes a proportional diminution and finally disappears. This new Tnes. ent Fig. 65.—Transverse section through a frog-embryo during the formation oi the medullary canal. c. coslome ; ect. ectoderm ; end. endoderm ; ent. enteron ; tnes. mesoderm ; mes^. its outer (parietal) layer; ntes^. its inner (visceral) layer; medullary fold ; medullary groove ; nch. notochord ; yk. yolk-cells. (After Marshall.) cavity, or archenteron (Fig. 64,1 and 65, en{), is the rudiment of the enteric canal: it begins to be formed as a narrow slit at the edge of the blastopore through which it at first communicates with the exterior, but it soon becomes closed : at present there is neither mouth nor anus. By this time the cells of which the embryo is composed have assumed different forms and become arranged in a. 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Parker, William Newton, joint author. London, Macmillan and Co. , Limited; New York, The Macmillan Company
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1900
