394 F. M. BALFOUR. 



Nuclei of primitive ova loith modijled nuclei — 



Granular 

 Nuclei. Bodies in Nuclei. 



0-018 mm O'OOS mm. 



0-016 mm 0008 mm. 



0-016 mm O'Oi mm. 



0-016 mm 



0018 mm 



These figures bring out with clearness the following points : (1) 

 that the modified nuclei are slightly but decidedly larger on the 

 average than the unmodified nuclei; (2) that the contained gran- 

 ular bodies are very considerablij smaller than ordinary nuclei. 



Soon after the appearance of the modified nuclei, remarkable 

 changes take place in the cells containing them. Up to 

 the time such nuclei first make their appearance the outlines 

 of the individual ova are very clearly defined, but subse- 

 quently, although numerous ova with but slightly modified nuclei 

 are still to be seen, yet on the whole the outlines of all the 

 primitive ova are much less distinct than before ; and this is espe- 

 cially the case with the primitive ova containing modified 

 nuclei. 



From cases in which three or four ova are found in a mass 

 with modified nuclei, but in which the outline of each ovum is fairly 

 distinct, it is possible to pass by insensible gradations to other 

 cases in which two or three or more modified nuclei arc found 

 embedded in a mass of protoplasm in which no division into 

 separate cells can be made out (fig. 14). For these masses I 

 propose to employ the term nests. They correspond in part with 

 the Ureier 71 ester of Professor Semper. 



Frequently they are found in hardened specimens to be en- 

 closed in a membrane-like tunic which apjjcars to be of the nature 

 of coagulated fluid. These membranes closely resemble and 

 sometimes are even continuous with trabecule which traverse the 

 germinal epithelium. Ovaries dificr considerably as to the time 

 and completeness of the disappearance of the outlines marking 

 the separate cells, and although, so far as can be gathered from 

 my specimens, the rule is that the outlines of the primitive ova 

 with modified nuclei soon become indistinct, yet in one of my 

 best preserved ovaries very large nests with modified nuclei are 

 present in which the outline of each ovum is as distinct as during 

 the period before the nuclei ujidergo these peculiar changes 

 (PI. XVIII, fig. 12). In the same ovary other nests are present 

 in which the outlines of the individual are no longer visible. The 

 section represented on PI. XVII, fig. 2, is fairly average as to 

 the disappearance of the outlines of the individual ova. 



It is clear from the above statements, that in the first in- 

 stance the nests arc produced by the coalescence of several pri- 



