400 THE FEMALE REPRODUCTIVE ORGANS 



frequently, however, the earliest step in the process consists in 

 the growth of solid cell columns from the layer of germinal epi- 

 thelium into the cortical stroma of the ovary. These cell columns 

 are known as P finger's tubes, though, except occasionally at the 

 extreme surface of the organ, they lack a true tubular form and 

 possess no vestige of a lumen. 



Certain cells in these columns, by their increased size and 

 prominent nucleus, become very early distinguished as the primi- 

 tive ova ; their differentiation is rapidly followed by the constric- 

 tion of the columns, through the activity of the surrounding tissue 

 of the stroma, in such a manner that one, rarely two or more ova, 

 and several undifferentiated epithelial cells are included in each 

 portion whose connection with the layer of germinal epithelium is 

 thus severed. In this way the primitive follicles (egg nests, or Ei- 

 ballen) are formed. In the ovary of the new-born hundreds of 

 such immature follicles occur in all portions of the cortex (Fig. 

 320). They are also found in large numbers in the ovary of the 

 adult, though it is asserted that during adolescence their forma- 

 tion gradually ceases. 



Many follicles never go beyond this primary stage of develop- 

 ment, but after a time undergo retrograde metamorphosis either 

 by gradual atrophy or by a process, known as atresia of the fol- 

 licle, in which the chromatolysis in the ovum and its surrounding 

 f ollicular cells is followed by growth and organization of the theca 

 f olliculi, the connective tissue which is thus formed finally replac- 

 ing the atresic follicle. 



After remaining stationary for a long period, often for years, 

 certain of the primitive follicles enter upon a period of rapid 

 growth. This process first affects the ovum and results in the 

 appearance of the deutoplasm, zona pellucida, and other accessory 

 structures, as already described under the development of the 

 germ cell. Cell multiplication now occurs in the surrounding 

 epithelial cells, so that, instead of the single row of epithelium 

 which surrounds the ovum of the primitive follicle, the ripening 

 follicle soon acquires a layer of follicular epithelium several cells 

 deep. 



The rapid multiplication of the epithelial cells is soon followed 

 by active secretion, resulting in the formation of a clear fluid by 

 which the cells are more and more separated, and the cytoplasm 

 of adjacent cells is then readily seen to be firmly joined together 

 by numerous delicate processes which may be regarded as intercelr 



