234 LILIAN SHELDON. 



Yig. 8. — Transverse section through the protoplasmic pole of an ovum, in 

 which the protoplasm extends over a larger area of the surface of the egg 

 than it did in the preceding figures. The protoplasmic segments are rather 

 more distinct from one another than they were in the preceding figures, but 

 are still connected by strands. Pm. S. Protoplasm segments. Y. S. Yolk 

 segments. V. m. Vitelline membrane, n. Nuclei. Oc. 2, obj. D. 



Fig. 9. — Section through half of an egg of about the same stage as that shown 

 in Fig. 8, in which the protoplasmic segments are more distinct from one 

 another than is usually the case. n. Nuclei. Pm. S. Protoplasmic segments. 

 Y. S. Yolk segments. V. m. Vitelline membrane. Oc. 2, obj. CC. 



Fig. 10. — Transverse section through an egg, in which the protoplasmic 

 segments have extended fully half-way round the periphery. The protoplasmic 

 areas are separated from one another by considerable tracts of yolk ; one area 

 lies quite at the surface, and contains a large round nucleus which appears 

 to be about to divide. Three protoplasmic masses are present in the central 

 yolk, one of which contains three chromatin particles. The yolk does not 

 appear to be segmented, but this may be due to the action of reagents. This 

 figure was compounded from two sections. Pm. S. Protoplasmic segments. 

 Y. Yolk. n. Nuclei. Oc. 2, obj. CC. 



Fig. 11. — Transverse section through the middle of an ovum, in which 

 there is a special area of protoplasm at one pole forming a reticulum, in 

 which many nuclei lie. Nuclei are also present scattered through the yolk. 

 The yolk is segmented. Pm. A. Protoplasmic area. Y. S. Yolk segments. 

 Oc. 2, obj. A. 



Fig. 12. — The protoplasmic area of the ovum shown in Fig. 11, more highly 

 magnified, to show the reticulate arrangement of the protoplasm, the absence 

 of cell outlines, and the irregular arrangement of the nuclei. Oc. 2, obj. D. 



Fig. 13. — Transverse section of an ovum, rather older than that from which 

 Fig. 11 was drawn. The protoplasmic area {Pm. A.) has become more com- 

 pact and flattened. The nuclei in the rest of the egg are more numerous 

 round the periphery than in the centre. The ovum is broken at two points. 

 Pm. A. Protoplasmic area. V. m. Vitelline membrane. Oc. 2, obj. A. 



Fig. 14. — The protoplasmic area shown in Fig. 13, more highly magnified, 

 to show the absence of cell outlines. Oc. 2, obj. D. 



Figs. 15 a — d. — Four transverse sections through the youngest ovum, in 

 which the embryo is definitely formed. Ec. Ectoderm, p. Cavity in the 

 proliferating mass of nuclei, p. n. Proliferating mass of nuclei, p. y. Peri- 

 pheral layer of yolk. V. m. Vitelline membrane. Y. Yolk within the embryo. 

 Oc. 4, obj. A. 



Fig. 15 a. Section through the anterior end of the ovum, in front of the 

 embryonic region, showing the segmented condition of the peripheral 

 yolk in this region. 



