. The biology of the frog. Frogs. 96 THE BIOLOGY OF THE FROG CHAP thick. The outer of these layers is the ectoderm ; the inner, the entoderm. The cells of the former are small and pig- mented ; those of the latter for the most part are compara- tively large, lighter in color, and contain a large amount of yolk. The two layers are continuous with each other at the lips of the blastopore. Before the process of invagination. BP BP' FlG. 20. — Sagittal section through a frog embryo. B, blastocoel; BP, dorsal lip of blastopore; BP', ventral lip of blastopore; EE, epidermic layer of ectoderm ; EN, i
. The biology of the frog. Frogs. 96 THE BIOLOGY OF THE FROG CHAP thick. The outer of these layers is the ectoderm ; the inner, the entoderm. The cells of the former are small and pig- mented ; those of the latter for the most part are compara- tively large, lighter in color, and contain a large amount of yolk. The two layers are continuous with each other at the lips of the blastopore. Before the process of invagination. BP BP' FlG. 20. — Sagittal section through a frog embryo. B, blastocoel; BP, dorsal lip of blastopore; BP', ventral lip of blastopore; EE, epidermic layer of ectoderm ; EN, inner or nervous layer of ectoderm ; H, hypo- blast or entoderm; T, mesenteron or gastrula cavity; Y, yolk plug. (After Marshall.) is completed there appears a third germ layer, the me so derm or mesoblast, between the other two. The mesoderm ap- pears all around the blastopore, and as this opening closes mainly from in front backward, the two masses of meso- derm on either side are brought near each other in the mid- dorsal line. The free ventral edges of the masses or sheets. 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 Holmes, Samuel J. (Samuel Jackson), 1868-. New York, London, Macmillan
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Keywords: ., bookauthorholmessamueljsamuelja, bookcentury1900, bookdecade1910