The American journal of anatomy . e knife. In the figures given every yolkgranule is faithfully drawn under the camera as accurately as pos-sible in its relations to the cell boundaries and nuclei. No yolkgranule is omitted because it seems to be displaced. ISTo drawings The Limit Between Ectoderm and Entoderm. 45 are taken from sections which show the slightest tearing or breakingin the parts concerned. 1. Early Form and Relations of completion of gastrulation the archenteron has the wellknown form, characteristic of amphibian embryos. The enlargedanterior part of the archenter
The American journal of anatomy . e knife. In the figures given every yolkgranule is faithfully drawn under the camera as accurately as pos-sible in its relations to the cell boundaries and nuclei. No yolkgranule is omitted because it seems to be displaced. ISTo drawings The Limit Between Ectoderm and Entoderm. 45 are taken from sections which show the slightest tearing or breakingin the parts concerned. 1. Early Form and Relations of completion of gastrulation the archenteron has the wellknown form, characteristic of amphibian embryos. The enlargedanterior part of the archenteron is bounded in the region where themouth will form by a relatively thin layer of entoderm and a thinnerlayer of ectoderm (Fig. 1). In this region are two broad, veryshallow depressions in the ectoderm. The more anterior one repre-sents the hypophysis, the posterior one the future mouth. Oppositethese the archenteron itself presents two prominent pits (or angles)as seen in sagittal sections. The anterior one is a slender pointed. mFig. 1. Amblystoma punctatum, neural plate stage, sagittal section of mouthregion. Borax carmine stain. cavity (Fig. 2), and the entoderm surrounding it forms a bluntwedge projecting between the neural plate and the ectoderm. Theposterior one is a broad depression which corresponds to the futuremouth opening. The entoderm surrounding the anterior pit isthe preoral entoderm and corresponds in every way to the preoralentoderm of most selachians (cf. Johnston, 1909). 4G J. B. Johnston. the neural plate rolls np into a tube (Fig. 2) pressure isexerted upon the archenteron by the brain portion of the neuraltube and the effed is seen in a compression of the archenteric two angles seen in sagittal sections are now more marked andare separated by a thickening or fold of the intervening the meantime the notochord and mesoderm are forming in thesame manner as in selachians. In the stages represented in Figs. 2and 3 the notochord en
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1910
