DEVELOPMENT OF FLUSTRELLA HISPIDA. 475 



Figs. 22, 23. — Sections of slightly older eggs in wlilcli the products of dis- 

 integration of the yolk nucleus have retreated towards the periphery of the 

 egg, there forming an open ring of deeply staining patches, each of which lies 

 within a clear space, x 400. 



PLATE 23. 



Fig. 24'. — Section of an egg showing the first appearance of the yolk in the 

 form of minute globules scattered in the protoplasm. All trace of the yolk 

 nucleus has vanished, x 400. 



Fig. 25. — Section of an egg in which the yolk is fully developed. The 

 section was stained with iron hsematoxylin, and the centres of many of the 

 yolk spherules remained stained even after prolonged washing, x 400. 



Figs. 26, 27. — Sections of eggs of about the same age as that illustrated in 

 figs. 14 and 15, and which have been treated with osmic acid. The yolk 

 nucleus is in immediate contact with the germinal vesicle, and the clear space 

 in which it usually lies is not present ; oil globules (01.) are present both in 

 the yolk nucleus and in the suirounding protoplasm, x 250. 



Pig. 28. — Section of an egg stained with osmic acid, in which yolk-forma- 

 tion is occurring. All trace of the yolk nucleus has vanished ; oil-drops are 

 scattered among the developing yolk, and are especially abundant towards tiie 

 periphery of the egg ; they may be distinguished by their darker colour. 

 X 250. 



Fig. 29. — Section through the germinal vesicle of a young egg. The 

 chromatic network is well developed, and darkly staining nodules are present 

 at its nodes. Lying at the edge of the germinal vesicle is a dark nodule (-T.A^.) 

 similar to those which occur at the nodes of the chromatin reticulum, and 

 which is apparently in process of passing out through the membrane of the 

 germinal vesicle to become one of the granules which will coalesce and form 

 the yolk nucleus. X 650. 



Fig. 30. — Section of the germinal vesicle showing the gradual attenuation 

 of the chromatin network as maturation proceeds. X 650. 



Figs. 31, 32. — Sections of the germinal vesicle in somewhat older eggs, 

 showing the increased size of the germinal vesicle and the attenuation of the 

 chromatin network. X 650. 



Fig. 33, — Section of the germinal vesicle showing the thickening of the 

 chromatin network which occurs in later stages, x 650. 



Fig. 34.— -Section of the germinal vesicle of an egg in which the formation 

 of the polar bodies will shortly take place. The chromatin network is much 

 thickened, and the substance between its meshes stains more darkly than at 

 earlier stajres. The nuclear membrane has become irregular, x G50. 



