SEGMENTATION OF THE EGG. 



SM i BA 



21 



SH 



sv 



FIG. 4. The Hen's Egg, freshly laid, x g. 



BA, germinal disc. SH, egg shell. SM, shell membrane. SV, air chamber. 

 ~WA, white or albumen. WC, chalaza. Y yolk. Z, vitelline membrane. 



FIG. 5. FIG. 6. 



FIGS. 5, 6. Stages in the segmentation of the germinal disc of the 

 Hen's Egg. x 10. (After Coste and Duval.) 



B ZL 



FIG. 7. Vertical section of the germinal disc of the Hen's Egg at 



the close of segmentation, x 25. (After Duval.) 



B, segmentation cavity or blastocoel. E, upper layer of blastomeres, or epiblast. 

 M"', nucleus of incompletely formed blastomere. VXi, vacuole in yolk. Y, yolk 

 ZL, lower layer of blastomeres. 



