Archive image from page 76 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 DEVELOPMENT PRIOR TO LAYING 59 germ-wall by the area with large granules Y. These zones con- stitute the opaque area. The circles in the pellucid area represent megaspheres, that is yolk-masses cut off from the floor of the subgerminal cavity and lying in the latter (cf. Fig. 28 M). The invaginated entoderm is represented by the crossed area E; the lip of the blastopore, where ectoderm and entoderm are continuous, by the region R. Fig.
Archive image from page 76 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 DEVELOPMENT PRIOR TO LAYING 59 germ-wall by the area with large granules Y. These zones con- stitute the opaque area. The circles in the pellucid area represent megaspheres, that is yolk-masses cut off from the floor of the subgerminal cavity and lying in the latter (cf. Fig. 28 M). The invaginated entoderm is represented by the crossed area E; the lip of the blastopore, where ectoderm and entoderm are continuous, by the region R. Fig. 3L—A diagrammatic reconstruction of the blastoderm repre- sented in Fig. 30. (After Patterson.) R., Mass of cells left after closure of blastopore. , Anterior portion of subgerminal cavity not yet crossed by the entoderm. Other abbreviations as in Fig. 29. The last three or four hours prior to laying witness the closure of the blastopore. A comparison of Figs. 27 and 29 will show that the blastopore has become considerably narrower in the later stage. It will be observed that the posterior ends of the germ-wall are approaching. Finally they come into contact, and the blastopore is closed. During this process the lip of the blastopore is not cut off externally, but on the contrary comes
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