DEVELOPMENT PRIOR TO LAYING 



51 



thus distinguish a syncytial, more peripheral, and a cellular, more 

 central, portion 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 central margin of the syncytial part of the 

 germ-wall becomes much less steep, owing apparently to active 

 proliferation of cells. This is illustrated in Fig. 25. Later yet 



BT 



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.) 



