File:Bailey031.jpg

Fig. 31. Median sagittal sections showing successive stages of gastrulation in the frog's egg

Bracket, from Kellicott.

A, beginning of gastrulation

B, slight advance in invagination and beginning of epiboly

C, invagination and epiboly progressing, inflection of cells (involution) occurring around dorsal lip of blastopore which is now an obvious structure

D, epiboly has resulted in covering of a large part of yolk by lip of blastopore

E, blastopore is now circular and filled with the yolk plug (cf. Fig. 30, A, 4) and the archenteron appears as a small space

F, the blastoccel is nearly obliterated

G, gastrulation completed.

a, Archenteron; b, blastopore; c, rudiment of notocord; ec, ectoderm; en, entoderm; gc, gastrular cleavage, ge, entoderm (protentoderm) ; m, peristomal mesoderm; np, neural plate; w/, transverse neural ridge; s, blastocoel.

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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the interpretation of developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these interpretations may not reflect our current scientific understanding. (More? Embryology History)

Reference

Bailey, F.R. and Miller, A.M. (1921). Text-Book of Embryology. New York: William Wood and Co.

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