OF THE VERTEBRATE OVARY. 561 



Unmodified nuclei of normal primitive ova 



o'oi 4 mm. 

 o'oi 6 mm. 

 o - oi4 mm. 

 o'oi6 mm. 

 o'oi 6 mm. 



Nuclei of primitive ova ivitJi modified nuclei 



Granular 

 Nuclei. Bodies in Nuclei. 



o'oiS mm o'ooS mm. 



ox>i6 mm O'ooS mm. 



o'oi 6 mm o'oi mm. 



ox>i6 mm. ...... 



o'oi 8 mm 



These figures bring out with clearness the following points : 

 (i) that the modified nuclei are slightly but decidedly larger on 

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

 granular bodies are very considerably 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 subsequently, 

 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 especially 

 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 are 

 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 Ureierncster of Professor Semper. 



Frequently they are found in hardened specimens to be 

 enclosed in a membrane-like tunic which appears to be of the 

 nature of coagulated fluid. These membranes closely resemble 

 and sometimes are even continuous with trabeculae which tra- 

 verse the germinal epithelium. Ovaries differ considerably as 



