1 46 MCMURRICH. 



EXPLANATION OF PLATE V. 



All the figures on this plate are oi Jaei-a marina. 



Fig. I. Transverse section of adult 9- Ow = ovary ; C^- = germinal region 

 of Ovary; ^ ^ chitinous portion of Spermatophore ; /) = intestine ; DC = 

 digestive ccecum ; N'= ventral nerve cord ; B = dorsal blood vessel. 



Fig. 2. Section of immature ovum showing protoplasmic network. For the 

 sake of clearness the yolk granules have been omitted, /c ^= follicle cells. 



Fig. 3. Section of mature ovum showing the peripheral and central proto- 

 plasm, the latter containing the nucleus. The network not visible. 



Fig. 4. Ovum just after the expulsion of the polar globules {/^) drawn from 

 living specimen. The dark structure in center is the segmentation nucleus with 

 its surrounding protoplasm seen indistinctly through the yolk, c/i = chorion ; 

 ym = yolk membrane. 



Fig. 5. Optical section of ovum in the two-celled stage. 



Figs. 6 and 7. Optical sections of ova in the four-celled stage showing differ- 

 ent stages in the rotation of the cells. 



Fig. 8. Ovum during the formation of the eight-celled stage. The figure is 

 from a cleared preparation so that all the nuclei are visible. 



Fig. 9. The eight-celled stage completed, from a cleared preparation. 



Fig. 10. Section of ovum in the eight-celled stage. 



Fig. II. Surface view of posterior pole of ovum in the i6-celled stage. The 

 two terminal endodermal cells are surrounded by a circle of seven cells. 



Fig. 12. Surface view of posterior pole of the i6-celled stage in which the 

 number of cells in the circle has been reduced to six. 



Fig. 13. Surface view of the 32-celled stage seen from ventral surface. 



Fig. 14. Surface view of the 64-celled stage seen from the side. 



Fig. 15. Surface view of posterior extremity of ovum passing into the suc- 

 ceeding stage. 



Fig. 16. Surface view of ovum in the succeeding stage seen from the side. 



Fig. 17. Ventral view of ovum in which the concentration of the cells towards 

 the ventral surface is taking place. 



Fig. 18. Dorsal view of the same ovum. 



Fig. 19. View of ovum in which the concentration is complete. 



Fig. 20. Longitudinal section of ovum in the 32-celled stage. 



