242 MARY BLOUNT. 



pression of Agassiz and Whitman (1). The periblast nuclei 

 migrate peripherally and also into subgerminal positions, and thus 

 we may speak of a marginal and central periblast. But the 

 nuclei of the central periblast have not been found in the nucleus 

 of Pander. 



In Lepidosteus osseus, Eycleshymer (2) found the nuclei most 

 numerous at the center, " undergoing rapid division and con- 

 tributing one derivative to the cell cap. 



Fig. 8 is a photograph of an egg obtained at 9:30 A. M., or 

 thirteen and a half hours after fertilization. The marginal cells 



Fig. 8. Photograph of pigeon's egg 13^ hours after fertilization, 9.30 A. M. An- 

 terior side of blastoderm toward point of arrow. 



are now limited peripherally, but are open below as is suggested 

 in Fig. 9, a transverse section through another egg of about the 

 same age. The periblast in such an egg as Fig. 8 is demon- 

 strated only in sections. It does not appear in surface view. 



7. The Growth of the Blastodisc at the Expense of the Periblast. — 

 In the teleost egg, after the conclusion of cleavage, the periblast 

 remains distinct from the blastodisc, but in the pigeon's egg, the 

 periblast continues to add cells to the segmented region. I have 

 studied this point carefully up to several hours after laying, but 

 have not completed my study on later stages of incubation. To 

 illustrate this, there is a series of drawings, Fig. 9 to Fig. 15. 



