PLATE 2 



EXPLANATION OF FIGURES 



5 Oocj^te, 400 x 376ju, at the beginning of the period of differentiation; oblique 

 view from the stigmal pole. The vascular network completely invests the oocyte 

 except in the region of the stigma (st.) which extends in the long axis. A direct 

 view in the polar axis showed the germinal vesicle near, but not quite at, the center 

 of the long axis. 



6 Oocyte, 902 X 829/x. Period of differentiation. Side view showing the differ- 

 entiation of the median vessel {m.v.). Note the germinal vesicle {g.v.) almost 

 central in position but slightly nearer to the animal pole, which is up, and to the 

 infundibular end of the long axis, to the left. 



7 Oocyte, 5.47 x 5.14 mm. magnified 15 diameters, at the end of the period of 

 differentiation, showing the stigma {st.) in the long axis, and the median artery 

 in somewhat oblique side view. The oocyte is free to rotate within the follicle 

 during this period and the germinal vesicle {g.v.) surrounded by segmental disc 

 and periblast {i>hl.) lies at one end of the long axis. This is an extreme case of 

 rotation; usually the rotation is around the long axis. Fig. 34 shows a stigmal 

 view of this oocyte. 



8 Animal pole of an oocyte of 3.2 mm. in median longitudinal section, X 100 

 diameters, Zeiss 16.0, oc. 6. An early stage in the formation of the blastodisc. 

 The germinal vesicle {g.v.) is surrounded by the fine granules of the segmental 

 disc, and this in turn by the periblast {phi.). The peripheral protoplasm {-p.p.) 

 is now a narrow zone. At the center of the germinal vesicle is the group of chro- 

 mosomes and nucleoli. 



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