210 WILLIAM WALLACE. 



Explanation op the Figures in Plates 15 — 17. 



h. c. Blood-corpuscles. b. v. Blood-vessel. cy. Cytoplasm. e. c. Egg 

 cavity, e. /. Degenerating egg. e;». Endothelium, e/?. Epithelium, gr.gr.' 

 Eollicular epitlieliuu>. g. v. Germinal vesicle, le. Leucocytes, ly. Lymph 

 space, m.p.f. Membrana propria folliculi. p. v. I. Zonoid layer, st. Stroma. 

 th. Theca folliculi. z. Definitive e^g membrane. 



PLATE 15. 



EiG. 1. — Zoarces. 13'2 cm. Eeb. 24. Section at the surface of an 

 ovary sliowing a "nest" of oogonia with interstitial cells. The compact, 

 rounded form of the nest indicates its origin from a single mother cell. All 

 the oogonia are equal in size and in the resting stage. Borax carmine. 

 X 400. 



Fig. 2. — Zoarces. 13*2 cm. Eeb. 24. A nest of oogonia with two de- 

 veloping ova, around which certain interstitial cells are already arranged, 

 forming a follicular epithelium. Note that there is no general fusion of the 

 oogonia to form a syncytium. Borax carmine. X 400. 



Fig. 3. — Zoarces. 15"5 cm. Sept. 18. Section of a nest with one de- 

 veloping ovum. Hermann's fluid and thionin. X 400. 



Figs. 4, 5. — Zoarces. 13"2 cm. Feb. 24. Nests composed entirely of 

 follicular epithelial cells and in contact with the germinal epiihelium. Their 

 derivation from the latter is indicated. There are no true ova in these nests. 

 Borax carmine. Zeiss D, ocular 4. 



Fig. 6. — Zoarces. 13"2 cm. Feb. 24. Section of young ovum showing 

 first appearance of the "yolk-nucleus" as a brightly staining cap applied to 

 one side of the germinal vesicle. Borax carmine. Zeiss A, ocular 4. 



Fig. 7. — Zoarces. 13'2 cm. Feb. 24. Section of developing ovum, 

 slightly larger than last. The "yolk-nucleus" has moved away from tlie 

 germinal vesicle, and is now spherical with reticular structure. The "centro- 

 sphere" (?) is also shown as a dark roundish body in contact with the 

 germinal vesicle, and looking like an extruded nucleolus. Borax carmine. 

 Zeiss A, ocular 4. 



F'iG. 8. — Zoarces. 13'2 cm. Feb. 24. Still larger ovum in section. 

 "Yolk-nucleus" seen as a circular zone of coarse fibrils in the cytoplasm. It 

 does not stain so intensely as in the earlier stages. The " centrosphere " (?) 

 also has moved outwards, and now lies in the "yolk-nucleus" zone. Borax 

 carmine. Zeiss A, ocular 4. 



I'iG. 9. — Zoarces. Section of developing ovum showing "yolk-nucleus" 

 around the germinal vesicle. Space between the yolk -nucleus and peripheral 

 protoplasm. Htemalum. Zeiss A, ocular 4. 



