16 



Mary Blount. 



mc -^ p 



G 



Fig. 10. — Diagrams of the posterior side 

 of longitudinal sections through a pigeon 

 egg about the time of the disappearance of 

 the sperm nuclei. A longitudinal median 

 section of the same egg is shown in Fig. 

 9. In 10 A, the marginal cell is continu- 

 ous with the periblast, as also at the left 

 of Fig. 9. Fig. 10 B is ten sections beyond 

 A, and here an indentation occurs which 

 in the second section beyond (Fig 10 C) 

 deepens into a cleavage furrow. In the 

 next section (Fig. 10 D) there are two 

 sperm nuclei in the accessoiy cleavage. 

 They are small and stain very faintly. 

 The wall separating one of the sperm 

 nuclei from the marginal cell has begun to 

 disappear. The other figures (Fig. 10 E, 

 F, G and H) show sperm nuclei either in 

 cells of accessory cleavage or in the margi- 

 nal periblast, and in either case they are 

 separated from the marginal cell. Through 

 all the sections of this egg, the marginal 

 cells are continuous with the periblast 

 except where sperm nuclei occur. All the 

 nuclei in this figure are sperm nuclei. 



a, cells of accessory cleavage. 



mc, marginal cell. 



p, mai'ginal periblast. 



