. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 296 CLEAVAGE (SEGMENTATION) AND BLASTULATION. Fig. 144. Cleavage in the rabbit egg. (After Gregory, '30.) (A) One-ceil stage. (B) Two primary blastomeres, one larger than the other. (C) Eight-cell stage. (D) Sixteen- cell stage. (E) Morula stage of 32 cells. (F) External view of stage approximating that in (G). (G) Inner cell mass and blastocoeiic cleft showing in embryo, about IV2 hours after copulation. (H) inner cell mass and blastocoeiic space
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 296 CLEAVAGE (SEGMENTATION) AND BLASTULATION. Fig. 144. Cleavage in the rabbit egg. (After Gregory, '30.) (A) One-ceil stage. (B) Two primary blastomeres, one larger than the other. (C) Eight-cell stage. (D) Sixteen- cell stage. (E) Morula stage of 32 cells. (F) External view of stage approximating that in (G). (G) Inner cell mass and blastocoeiic cleft showing in embryo, about IV2 hours after copulation. (H) inner cell mass and blastocoeiic space in embryo, approxi- mately 90 hours after copulation. Entoderm cells have not yet appeared. pigment cells is marked toward the end of the blastular period and during gastrulation. Cf. figs. 141H-L; 142H-L. The blastocoel within the mass of blastomeres of the cleaving egg of the frog forms somewhat differently from that in Amphioxus in that the cavity arises nearer the animal pole. The smaller micromeres of the animal pole, therefore, are more directly involved than the macromeres of the vegetal pole. Beginning at the eight-cell stage, a spatial separation is present between the four micromeres at the animal pole. The floor of this space or beginning blastocoel is occupied by the yolk-laden macromeres (fig. 143A, B). As development proceeds, this eccentricity of position is maintained, and the. 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 Nelsen, Olin E. (Olin Everett), b. 1898. New York, Blakiston
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