122 J. T. CQNNINGHAM. 



by an aborted egg in the ovary of a plaice 12j inches long, 

 examined at Lowestoft on September 21st, 1895, The egg 

 has evidently died at a very early stage, when scarcely any 

 yolk had been deposited, and consequently it is not very 

 opaque. It appears also to have only recently died, and there- 

 fore to have undergone but little of the process of retrogres- 

 sive change. The nucleus, ik will be seen, shows an irregular 

 indistinct outline, and a single nucleolus towards the centre. 

 The appearance of this aborted egg presents a marked contrast 

 with that of the three normal younger eggs figured with it. 



The History of the Germinal Vesicle and Yolk 



Nucleus. 



To give a complete histoi'y of these structures and their 

 relations to one another, it would be necessary to follow con- 

 tinuously the history of the egg from its origin in the germinal 

 epithelium onwards. But unfortunately it is very difficult to 

 obtain a distinct and definite view of the parts of the young 

 ova in their earliest stages, in consequence of their small size 

 and the indefiniteness of the limits between different eggs and 

 different parts of each egg. I have endeavoured to trace the 

 origin of the ova in the germinal epithelium, both in the 

 ovaries of very young immature fish and in the spent ovaries 

 of mature fish, at the stage in which the new crop of ova is 

 beginning its development. Up to the present I have not 

 succeeded in tracing satisfactory indications of the division of 

 the germ-cells by which the ova must be produced, nor have I 

 been able to detect the yolk nucleus in the very young ova still 

 within the germinal epithelium, or but recently separated 

 from it. 



If indirect or mitotic division of the nucleus were universal, 

 or if it occurred at least in all undiff'ereutiated rapidly mul- 

 tiplying cells, it ought to be the mode in which the germ-cells 

 divide in the germinal epithelium. We know that it occurs 

 and is obvious and conspicuous enough in the division of 



