24 EMBRYOLOGY OF THE LOWER VERTEBRATES ch. 



eventually results a blastula (A 5) the upper portion of which, 



forming rather less than a hemisphere, is composed of micromeres 



while the lower part is composed of large, richly yolked, macromeres. 



In Amia the " oval "-shaped egg measures about 2-5-3 mm. by 



Fig. 14. — Segmentation in Acipenscr (A), Amia (B), and 

 Lepidnsteus (C). (After Bashford Dean, Eycleshyiner, 

 and Whitman. ) 



A 1, 2 and 3, 13 1 and '2, C 1 and 2 are views of the apical pole : the 

 remaining figures are side views. 



about 2-2-5 mm. In the region of the apical pole which lies at the 

 end of the long axis is a cap-shaped portion richer in protoplasm — 

 an approach in fact to a germinal disc — while the rest of the egg 

 is rich in dark grayish brown yolk. 



The segmentation (Fig. 14, B) begins, about an hour and a half 



