OVULATION. 23 



brane with widely scattered nuclei. The discus proligerus is already 

 separated from the rest of the granulosa, and its cells, except those con- 

 stituting the corona radiata, which still show the radial arrangement 

 about the egg, are becoming detached from one another. As in the other 

 two follicles, the first polar cell has been produced, and the second 

 spindle (not shown in the drawing) is fully formed. There is a small 

 space between the zona pellucida and the vitellus. 



In fig. 39 (plate 6) the contents of the follicle have begun to flow 

 out into the periovarial space through an opening at the surface of the 

 ovary. The opening does not have the appearance one would expect 

 to result from a rupture due to pressure from within, but rather from a 

 condition produced by the migration of cells away from the rupturing 

 region. The viscidity of the fluid is indicated by the sinuous, more or 

 less parallel, line-like markings of the escaping contents (see also Sobotta, 

 1895) , and the plasticity of the discus cells is shown by the partial oblitera- 

 tion of the radial arrangement of the corona cells around the egg. The 

 distance between zona and vitellus is so much increased on the deep 

 side of the egg that the polar cell lies in the space thus formed quite free 

 from contact with either. 



In the last stage (fig. 40) the egg lies in the periovarial space, the 

 follicle having collapsed. Here, too, there is the same lack of evidence 

 of a violent tearing of the follicle wall. The contents of the follicle still 

 have the appearance of a viscous substance. The flattening of the egg, 

 probably caused by unequal pressure perhaps due to the narrowness 

 of the space between the ovarian capsule and the wall of the ovary- 

 suggests considerable plasticity. This condition can also be seen sub- 

 sequently in eggs which lie between ridges of the oviduct. The zona is 

 separated from the vitellus, as in the preceding stage, and the polar 

 cell is detached from the egg, though not shown in fig. 40. 



The corona cells surround the egg in its passage to the oviduct and 

 persist for a varying number of hours. 



