DEVELOPMENT PRIOR TO LAYING ol 
entoderm and the periblast proper as well. We shall follow this 
usage and distinguish two parts of the germ-wall. 
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 
A 
Fiq. 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.) 
