OVARY AND OVARIAN OVA IN CERTAIN MARINE FISHES. 145 



sections it is seen to be more or less wrinkled^ folds of it 

 projecting inwards between the nucleoli. This is not a con- 

 dition produced entirely by the action of the fixing reagents. 

 I have often observed in perfectly fresh material that the surface 

 of the vesicle instead of being smooth consisted of numerous 

 bulbous projections, as seen in fig. 25. In consequence of this 

 condition it frequently happens that a nucleolus appears in a 

 section to be outside the vesicle^ wheu examination of consecu- 

 tive sections shows that it is really contained in a pocket or 

 diverticulum of the vesicular membrane. This is, I believe, 

 one of the circumstances that have led observers to describe the 

 migration of nucleoli from the vesicle into the external cyto- 

 plasm. It is^ however, certain that during the period now 

 under consideration the nucleoli migrate from the periphery to 

 the central region of the vesicle, where they are for the most 

 part found around the tangle of fibrils, though some are scat- 

 tered among the fibrils. Fig. 26 shows a section of a vesicle 

 from the same preparation as fig. 25 in an ovum '39 mm. in 

 diameter, in which the yolk is at the stage seen in fig. 15, PI. 2. 

 The ovum figured being near the edge of the preparation, 

 where the osmic and chromic acids have acted most strongly, 

 the fibrils are not well stained, and are therefore less distinct ; 

 the reticular appearance of the achromatic substance is, on the 

 other hand, conspicuous. Fig. 27, PI. 4, shows the appearance 

 of the vesicle of an ovum "36 mm. in diameter, in a section 

 fixed from material with picro-sulphuric acid, the material being 

 a portion of the same ovary of plaice from which the chromosmic 

 sections were derived. The vesicle itself is '16 mm. in its 

 longest diameter. The section was stained with Delafield's 

 hsematoxylin. The fibrils are distinct, but appear at this 

 stage to form a continuous convoluted thread, a true spirem, 

 not a number of separate chromosomes. 



I have not been able to follow out the history of the ger- 

 minal vesicle in the later stages in the plaice and flounder, and 

 must therefore proceed to the description of certain stages 

 which I have examined in other species. In figs. 10, 11, 12, PI. 2, 

 will be seen the appearance of the vesicle in various stages of 



VOL. 40, PART 1. NEW SEE. K 



