Archive image from page 74 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 DEVELOPMENT PRIOR TO LAYING 57 anterior position in the entoderm (Patterson). But after the margin has thickened the farther extension of the entoderm is due, largely at least, to ingrowth from the marginal thickening Patterson also believes that the thickening of the margin is due not so much to multiplication of cells in situ as to immigration of cells from the sides. This view is also supported by experi- ments. S G D F H Fig. 29.
Archive image from page 74 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 DEVELOPMENT PRIOR TO LAYING 57 anterior position in the entoderm (Patterson). But after the margin has thickened the farther extension of the entoderm is due, largely at least, to ingrowth from the marginal thickening Patterson also believes that the thickening of the margin is due not so much to multiplication of cells in situ as to immigration of cells from the sides. This view is also supported by experi- ments. S G D F H Fig. 29. — Diagrammatic reconstruction of the blastoderm of a pigeon's egg, 36 hours after fertihzation; from the same series as Fig. 28. X (After Patterson.) V'cZr''' T ''n tderm. 0., Margin of overgrowth. PA., Outer margin of pellucid area. R., Margin of invagination Y Yolk ?onI br'7P'''\ ••' -SS of olk-sac entoderm 1., lolk zone. Z., Zone of junction. The arrows at the posterior margin indicate the direction of movement of the halves of the margin. The circles in the peHucid area indicate yolk masses in the segmentation cavity. P' Figure 29 is a reconstruction of a blastoderm in the stage of Fig. 28, that is at the height of gastrulation. The margin of overgrowth (cf. Fig. 28 O) is represented by the area Q- the zone of junction by the ruled area Z; the inner portion of the
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