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Vertical section of blastoderm of chick (1st day of incubation). S, epiblast consisting of short columnar cells; D, hypoblast, consisting of a single layer of flattened cells; M, formative cells." They are seen on the right of the figure, passing in between the epiblast and hypoblast to form the mesoblast; A, white yolk granules. Many of the large "formative cells" are seen containing these granules.

Blastoderm of a Chick

Vertical section of blastoderm of chick (1st day of incubation). S, epiblast consisting of short columnar…

Vertical section of area pellucida and area opaca (left extremity of figure) of blastoderm of a fresh laid egg (unincubated). Labels: S, superficial layer corresponding to epiblast; D, deeper layer, corresponding to hypoblast; and probably in part to mesoblast; M, large "formative cells," filled with yolk granules, and lying on the floor of the segmentation cavity; A, the white yolk immediately underlying the segmentation cavity.

Blastoderm of an Egg

Vertical section of area pellucida and area opaca (left extremity of figure) of blastoderm of a fresh…

A transverse section through an embryo chick (26 hours). Labels: a, epiblast; b, mesoblast; c, hypoblast; d, central portion of mesoblast, which is here fused with epiblast; e, primitive groove; f, dorsal ridge.

Cells of an Embryo Chick

A transverse section through an embryo chick (26 hours). Labels: a, epiblast; b, mesoblast; c, hypoblast;…

"Further development of hen's egg; after Haeckel: A, the mulberry mass of cleavage cells, b, same as seen on top in fig 111, F, here viewed in profile in section, resting upon n, the simply-shaded part of the figure, to represent conventionally the mass of food-yelk. A, morula stage (as before); B, blastula stage, the mass of cells, b, forming the blastoderm, uplifted from the food-yelk, leaving the cleavage-cavity, s; w, the thickened rim of the germ-disc; C, the blastula in process of inversion, by which a layer of entoderm-cells, i, growing from periphery to centre, will apply itself to the layer of exoderm-cells, e, obliterating the cleavage-cavity, s; D, the disc-gastrula completed, by union of entoderm, i, with exoderm, e, leaving the primitive intestinal cavity, d, which is quite similar in appearance to the cleavage cavity, s, but morphologically quite different." Elliot Coues, 1884

Egg Germination

"Further development of hen's egg; after Haeckel: A, the mulberry mass of cleavage cells, b, same as…