OOGENESIS IN THE WHITE MOUSE 265 



IroD hematoxylin (Heidenhain's) was used for staining most 

 of the; sections, and for bringing out the details of the chromatin 

 it can hardly be improved. Flemming's triple, usually one of 

 the shorter methods, was used with Flemming fixed material 

 in a number of cases, and proved very useful in bringing out the 

 nucleoli and the idiosome. 



A large number of ovaries of different ages were also fixed and 

 stained for mitochondria. Benda's own method was used, with 

 varying success. More reliable and certain, and better in several 

 ways, is the following method: the tissue is fixed in Benda's 

 fluid (Flemming's, with about one drop of glacial acetic acid to 

 each 10 cc.) or Helly's, or Zenker's fluid (with the acetic acid 

 reduced as above) and then mordanted in 2-2.5 per cent potas- 

 sium dichromate for two to four weeks, the longer time being 

 perhaps preferable. Sections are stained with Weigert's copper 

 hematoxylin. Tissues fixed in Benda's fluid with no subsequent 

 mordantage, and stained with copper hematoxylin also gave 

 very good results. By this method the mitochondria are stained 

 black or blue-black and stand out very clearly against the 

 yellow background of the cytoplasm. 



MORPHOGENESIS OF THE OVARY 



In the development of the cat's ovary, von Winiwarter and 

 Sainmont ('08) describe two proliferations of cells from the 

 germinal epithelium before birth, forming medullary and cortical 

 cords respectively, and lay some emphasis on these as separate 

 down-growths. The germ cells and follicle cells of the first 

 proliferation and the germ cells of the second all degenerate by 

 the time the kitten is a few months old. At the age of about 

 three and a half or four months, by a renewal of the activity 

 of the germinal epithelium, a third proliferation of cells occurs, 

 from which develop the definitive egg-cells or ova, making up 

 the definitive cortex of the ovary. Kingsbury ('13) does not 

 distinguish between a first and a second proliferation of cells 

 in the embryo, considering them parts of one continuous process. 

 From the cells which arise first from the germinal epithelium are 

 formed the 'medullary cords,' and the 'cortical cords' or tubes of 



