256 BUMPUS. 



EXPLANATION OF PLATE XVI. 



Fig. 1. A median cross-section through an ovarian egg. The stage is compara- 

 ble with A, PI. XIV. A protoplasmic mass is shown at I. in., while on the right of 

 the figure is seen a section of the smaller division of the egg. 



Figs. 2, 3. Surface views of the closing blastopore. X 60. 



Figs. 4-6. Cross-sections through planes represented on Fig. 13. X 200. The 

 ectoderm is colored deep gray, while the entoderm is represented in a lighter shade, 

 extending indefinitely into the yolk. 



Figs. 7, 8. Highly magnified sections through the ovarian egg. 



Fig. 9. A diagram illustrating the migration of the segmentation nuclei towards 

 the surface, and the formation of the blastomeric " hills." Five nuclei are shown in 

 the upper part of the egg, while in the lower portion only a single nucleus is repre- 

 sented. 



Fig. 10. Enlarged figure of the portion of the ovary represented in Fig. 12. 

 X 200. 



Fig. 11. Section through an older ovary. X 55. 



Fig. 12. Cross-section through an immature ovary. X 55- Fig. 10 represents a 

 portion of same considerably enlarged. 



Fig. 13. Longitudinal section through egg of same stage as represented in PI. 

 XIV., Figs. H-I. X 200. 



