DEVELOPMENT PRIOR TO LAYING 



51 



entoderm and the periblast proper as well. We shall follow this 

 usage and distinguish two parts of the germ-wall. 



1 



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FIG. 24. Part of the margin of a horizontal section 

 through the blastoderm of a pigeon's egg about 25 hours 

 after fertilization (8.50 P.M.). (After Blount.) 

 1, Periblast nuclei. 2, 3, Cells organized in the periblast. 



4, A cell apparently added to the blastoderm from the 



periblast. 5, Vacuoles. 



In later stages the inner margin of the periblast becomes much 

 less steep, owing apparently to active proliferation of cells. This 

 is illustrated in the outline drawings of Fig. 25. Later yet the 



FIG. 25. Outlines of the margins of transverse sections 

 of the blastoderm of pigeon's eggs; 26 (A), 28 (B), and 

 32 (C) hours after fertilization. (After Blount.) 



