PLATE 4 



EXPLANATION OF FIGURES 



Photogruphh! from the same series of sections used for plate 3. 



19 Oocj'te, 293 x 27(V, cut in the long and polar axes. Zeiss 4 mm., oc. 4, 

 reduced to X 280. From a free hand section stained with Sudan in. The spher- 

 ules are disappearing from the central protoplasm and one can begin to distinguish 

 a spherule zone (s.c.) within the periplioral protoplasm (p.p.). The size relations 

 between germinal vesicle (g.v.), and ooplasm are noteworthy in comparison with 

 the oocytes sectioned in paraffin e.g., fig. 20. 



20 Oocyte, 354 x 324 ju ; magnification as in fig. 19. End of second growth i)eriod 

 Cut in long and polar axes. The persistence of the center of the yolk nucleus 

 iy.tt.), at this stage is a condition found only occasionally. 



Period of differentiation. 

 Figs. 21 to 2.5 were taken with a Zeiss 8 mm. apochromat, oc. 2, and reduced to 

 X 80. 



21 Oocyte, 512 x 400/u, cut near the animal pole. Photographed from a fi'ozen 

 section, 50ju thick, stained with Sudan. At this stage the spherules form a zone, 

 (s.2.), near the periphery, but with a higher power the clear peripheral protoplasm 

 can be distinguished. The alveolar appearance is an artefact flue to freezing. 

 Only the tip of the germinal vesicle (g.v.) appears. 



22 Oocyte, 762 x 710/^, cut perpendicular to the polar axis, showing the ger- 

 minal vesicle nearer one end (left) of the long axis. The central and peripheral 

 protoplasm (p.p.) can be distinguished with the spherule zone between them. 



23 Oocyte, 786 x 762ju, cut in the long and polar axes, in about the same stage 

 as fig. 6. At the right the section passes to one side of the stigma (sL). The 

 spherule zone {s.z.) can be seen and in addition many large definitive yolk granules 

 have appeared throughout the ooplasm. 



24 Oocyte, 1.06 x 0.89 mm., cut in long and polar axes. The germinal vesicle 

 has migrated peripherally out of the central protoplasm, the boundary of which is 

 marked hz. 



25 Oocyte, 1.17 in long axis, cut in the polar axis and obliqueh' to the long axis. 

 The photograph was taken from a section nearer to one end of the long axis. The 

 central and peripheral protoplasm and a single spherule zone may be distinguished 

 (more clearly on the right). The definitive yolk granules are especially numerous 

 peripherally. 6.2, boundary of the central jirotoplasin. 



320 



