OVARY AND OVARIAN OVA IN CERTAIN MARINE FISHES. 125 



for about fifteen hours. The largest eggs in these sections are 

 •15 mm. in diameter. In these the vitelline nucleus is dis- 

 tinct. The form of the egg is well preserved. The cytoplasm 

 is very homogeneous in appearance, and exhibits no trace of 

 yolk or of granular texture. The vitelline nucleus is situated 

 close to the periphery of the egg, and consists of a rounded 

 stained mass containing vacuoles in its substance. Its limit 

 from the cytoplasm is not perfectly definite, as it is evidently 

 continuous with the substance of the latter. The germinal 

 vesicle is somewhat excentric in position in the egg, has a 

 distinct membrane, and a number of small nucleoli arranged 

 at nearly equal intervals inside the membrane. The reticulum 

 of the internal cavity of the nucleus is extremely fine, and 

 takes stains very slightly. The smallest egg in which I have 

 seen the vitelline nucleus in these sections is '08 mm. in 

 diameter, and in this case it is also situated at some distance 

 from the germinal vesicle. I have not been able to make it 

 out in any egg in contact with the membrane of the germinal 

 vesicle, although it is seen in that position, in what is evi- 

 dently its earlier stage, in fresh material treated with acetic 

 acid on the slide. I am obliged to conclude, that although 

 the preservation of the material in the sections above described 

 appears to be excellent, yet the mixture of chromic and osmic 

 acid mentioned is not capable of differentiating the vitelline 

 nucleus in the earlier stages of its history, and of demonstrat- 

 ing its origin. In these sections, as in those previously men- 

 tioned, the germinal epithelium is thin, flat, and indistinct, so 

 that it is vain to attempt to trace the origin of the ova 

 from it. 



In the ovary of a mature flounder which had spawned in 

 March, and which was killed on July 11th, it is evident from 

 the sections that the production of the new crop of ova from 

 the germinal epithelium was going on. At numerous points 

 in the epithelium are seen groups of germ-cells, consisting of 

 two or more, each having an oval shape in section, and con- 

 taining a large nucleus, which in structure is similar to that of 

 the smallest eggs described in the ovary of the plaice 3 inches 



