266 H. M. KINGEHY 



Pflijger are formed later, outside of or peripheral to these; and 

 medullary are not to be sharply distinguished from cortical 

 cords. Kingsbury also found no evidence of a third or post 

 foetal proliferation of cells shortly before sexual maturity. 



In the mouse there is a single continuous proliferation of cells 

 from the germinal epithelium which extends up to about birth. 

 This proliferation of cells does not take the form of tubular 

 'down-growths/ as in the cat and other forms, but the cells are 

 in irregular masses just beneath the epithelium. Later, as the 

 ovary grows in size and the stroma cells increase in number, 

 these latter tend to wander in and break these masses of cells 

 into short, thick structures which are, however, imperfectly 

 and incompletely separated from each other (fig. 9). The small 

 size of the ovary may be responsible for this pattern in the de- 

 velopment; there is not enough room for the formation of the 

 pronounced cords or egg-tubes found in other larger forms. 

 These groups of cells are not at first separated from the germinal 

 epithelium, but with the development of the tunica albuginea 

 these cell-masses become cut off about the time of parturition. 

 The development of the tunica will be taken up later. As was 

 stated above, this process of cell-formation is a continuous proc- 

 ess in the mouse; there is no distinction to be made between a 

 first or medullary and a second or cortical proliferation. The 

 inner regions of these cell-masses or groups might be termed 

 'medullary,' and what might be called 'medullary follicles' are 

 probably formed by the separation of some of the germ cells 

 with their follicle cells from these masses. These 'medullary 

 foUicles' would contain cells formed first from the germinal 

 epithelium, which consequently are further along in development 

 than those more peripherally located. 

 • There is a small amount of stroma in the ovary at this time, 

 formed by the differentiation and multiplication of mesenchymal 

 cells which have wandered in at the hilum. Blood vessels are 

 present as a few capillary loops. The stroma cells, as mentioned 

 above, grow peripherally in strands and partially separate the 

 cell-masses from each other (fig. 9). These stroma cells, on 

 reaching the base of the germinal epithelium, begin to grow 



