Archive image from page 72 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 DEVELOPMENT PRIOR TO LAYING 55 The margin of invagination is known as the Hp of the blasto- pore or primitive mouth; the space between this margin and the yolk is the blastopore, and the space between the entoderm and yolk, derived from part of the subgerminal cavity, is the archenteron or primitive intestine. Fig. 27. — Diagrammatic reconstruction of the blasto- derm of which a longitudinal section is shown in Fig. 26. C-D., Plane of
Archive image from page 72 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 DEVELOPMENT PRIOR TO LAYING 55 The margin of invagination is known as the Hp of the blasto- pore or primitive mouth; the space between this margin and the yolk is the blastopore, and the space between the entoderm and yolk, derived from part of the subgerminal cavity, is the archenteron or primitive intestine. Fig. 27. — Diagrammatic reconstruction of the blasto- derm of which a longitudinal section is shown in Fig. 26. C-D., Plane of Fig. 26. •' W;' perm-wall. 1, 2, 3, 4, 5, 6, and 7 indicate regions of the blastoderm which are approximately from 1 to 7 cells deep respectively. The broken line around 1 indicates the region where the blastoderm is approxi- mately one cell deep, x (After Patterson.) The first stage in the formation of the entoderm is interpreted as involution of the free margin, and this view is supported by the fact, determined by Patterson, that the antero-posterior diameter of the blastoderm is shorter than the transverse diameter during this process, whereas previously the blastoderm was approximately, circular. An even stronger support of this view IS turnished by experiments which demonstrate that injuries to the margin made just prior to gastrulation appear later in an
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