362 



two are biovular and of the remainder not more than 10 per cent. 

 All these abnormal follicles agree in certain particulars. They all 

 contain two egg-cells, a larger number was not found in any follicle. 

 The two ova are equally developed, thus differing from some of 

 those recorded by tan Beneden (4) and Honore (9), where they are 

 ia different stages of development. Again the two egg-cells are 

 always closely apposed one to the other even in the youngest pri- 

 mordial follicles whereas in those described by Schrön (20) and 

 HoNORE (9) each ovum is completely surrounded by the cells of the 

 nierabrana granulosa. 



A number of the biovular primordial follicles were found gener- 

 ally situated in the stroma of the ovary just beneath its external 

 epithelium. The ova are hemispherical in form and the flat side of 

 each is in close apposition to that of its fellow so that there is no 

 room for the follicular cells to interpenetrate between them. In the 

 very young stages the zona pellucida has not begun to form so that 

 the two egg-cells are actually touching in the middle line (fig. 6). 

 Each ovum possesses a well defined nucleus with a distinct membrane 

 and a conspicuous nucleolus and its granular cytoplasm differs in no 

 way from that of the normal egg. Like the latter also, the ova are 

 surrounded by somewhat flattened epithelial cells the forerunners of 

 the membrana granulosa and have as yet no conjunctive theca. The 

 biovular follicles are readily recognisable even at this stage, for, no 

 matter how tightly the ordinary ovules may be packed together they 

 are always separated by a thin layer of epithelial cells (fig. 7). 



At a slightly later stage (fig. 8) the epithelial cells have in- 

 creased in number and now form a well marked unicellular layer 

 whose cells take the form of short cylinders. These cells are now 

 more clearly marked off from the surrounding stroma by the presence 

 of a very thin membrane, the beginning of the membrana propria, 

 although here again the theca has not been developed. The two eggs are 

 now more sharply defined as each is surrounded by an extremely thin 

 zona pellucida. They are however still closely apposed and it appears 

 impossible that the follicular cells could have penetrated between them. 



At a still later stage we find follicles which are quite typical 

 save that instead of the single centrally placed ovum there are two 

 ova quite closely pressed together. These ovules are each surrounded 

 by a well marked zona pellucida. Outside them the follicular cells 

 have increased in number and form a multicellular layer, the membrana 



