SO-CALLED PARTHENOGENESIS IN THE WHITE MOUSE. 249 



for some time after the oocyte itself has completely degenerated 

 and disappeared, although in a few instances it is absorbed early. 

 Phagocytic (?) cells make their way into the oocyte through the 

 zona pellucida, and are probably to be regarded as follicle cells 

 from the degenerating follicle. These cells are usually seen in 

 the outer border of the oocyte, or just outside it, lining the 

 inner surface of the zona pellucida, sometimes as early in the 

 course of degeneration as the spindle stage. There are not many 

 of these cells in a single oocyte, not more than eight or ten and 

 frequently no more than three or four. They may be imbedded 

 in the cytoplasm of the egg-cell and in the "morula" stage are 

 frequently seen in between the separate cells. One case is 

 illustrated (Fig. 14) showing one of these extra-ovular cells just 

 after it has entered the oocyte, still retaining its connection with 

 other follicle cells outside the egg-cell by means of a protoplasmic 

 process extending through the zona pellucida. This same cell 

 is also shown to be connected with one or two other similar cells 

 within the zona by other protoplasmic processes, forming a 

 sort of syncytial net-work or mesh-work in among the fragments 

 of the degenerating egg-cell. 



The cytoplasm of these cells is usually rather scanty and 

 sometimes they look like bare nuclei imbedded in the cytoplasm 

 of the oocyte (Figs. 8 and 9). They are not, however, to be 

 confused with the nuclei of the oocyte formed by the breaking 

 down of the spindle, for they react differently to the stains used 

 and have a different structure. They are finely granular and 

 these granules are stained an intense black by iron hematoxylin 

 and deep blue by Jenner's stain. 



It may be through the action of these cells that the fragments 

 of the oocyte are gradually absorbed and disappear, for later 

 on the zona pellucida is seen, shrunken and distorted, with a 

 few of these cells in a remnant of the egg-cell. In still later 

 stages, these cells are seen alone inside the zona, and this condi- 

 tion may persist for some time (Fig. 16). Eventually the zona 

 pellucida and these cells all disappear and by this time the 

 follicle itself has usually completely degenerated. 



Thus it is seen that the oocytes in atretic follicles in the ovary 

 of white mice not yet sexually mature undergo a series of changes 



