. The development of the chick; an introduction to embryology . on ( ). (AfterBlount.)1, Nests of periblast nuclei. 2, Periliiast nucleus in marginal , Syncytial mass derived presumal:i!y from the periblast, in process of or-ganization into cells. 4, Vacuoles. Some phases of these processes are illustrated in Figs. 23 and24. In the vertical section. Fig. 23, the surface of the germ-wall next the blastoderm is indented as though for the formationof superficial cells. Along the steep central margin of the germ-wall groups of (-ells are apparently being cut off and added tothe c
. The development of the chick; an introduction to embryology . on ( ). (AfterBlount.)1, Nests of periblast nuclei. 2, Periliiast nucleus in marginal , Syncytial mass derived presumal:i!y from the periblast, in process of or-ganization into cells. 4, Vacuoles. Some phases of these processes are illustrated in Figs. 23 and24. In the vertical section. Fig. 23, the surface of the germ-wall next the blastoderm is indented as though for the formationof superficial cells. Along the steep central margin of the germ-wall groups of (-ells are apparently being cut off and added tothe cellular blastoderm. In the horizontal section, Fig. 24, theprocess of celhilarization at the central margin of the germ-wallis api)arently proceeding rapidly. The sui)erficial cells thus added to the margin of the cellularl)lastoderm become continuous with the ectoderm, and thedeeper layers later form the yolk-sac entoderm which becomescontinuous with the embryonic entoderm secondai-ily. Tlie termgerm-wall is usuall\ applied to the piiiuordium of the yolk-sac. DEVEL()PMP]NT PRIOR TO LAYIXO 51 entoderm and the peril)last proper as well. We shall follow thisusage and distinguish two ])arts of the germ-wall. I <*^ .Av.«* * Fig. 24. — Part of the inaririn of a horizontal .sectionthroutrh the l^ of a pigeons egg about 25 hoursafter fertiUzation ( ). (After Blount.)1, Periblast nuclei. 2, 3, Cells organized in the periblast. 4, A cell a}iparently added to the blastoderm from the periblast. 5, Vacuoles. In later stages the inner margin of the periblast becomes muchless steep, owing apparently to active proliferation of cells. Thisis illustrated in the outline drawings of Fig. 25. Later yet the
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Keywords: ., bookcentury1900, bookdecade1900, bookiddevelopm, booksubjectbirds
