DEVELOPMEXT PRIOR TO LAYIXG 



49 



served that the large marginal cells on each side are continuous 

 with the periblast, and nuclei are found in the periblast both 

 central and peripheral to the zone of junction. The latter forms 



,u.^=,^^ 



j00^^^t^^ik^ 



» ,s. 



I 



Fig. 21. — Longitudinal section of the blastoderm of a pigeon's egg at the 

 time of disappearance of the sperm-nuclei. On the left (anterior) margin, 

 the marginal cells have become open, that is, continuous with the peri- 

 blast, as contrasted with Fig. 20. About 11 hours after fertilization (7.00 

 A.M.). (After Blount.) 



1, Marginal cells. 2, Cone of protoplasm. 3, Marginal periblast. 4, Neck 

 of latebra. 5, Yellow yolk. 



Fig. 22. — Transverse section through the center of the blastoderm of a 



pigeon's egg, 14^ hours after fertilization (10.30 a.m.). (After Blount.) 



1, Marginal cells. 2, Marginal periblast. 3, Nuclei of the subgerminal 

 periblast. 



