CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 39 
were obtained had been ascertained. In each case the entire 
ovary was cut into serial sections. 
During the progress of our work-new problems arose and an 
accident made it impossible for us to re-examine all our material 
in order to answer several questions which were raised at a 
later stage of our investigation. We especially regret our in- 
ability to determine the existence of follicles which were ready 
to rupture, in certain cases in which these data would have been 
of considerable interest. Our work is therefore incomplete in 
some respects. We expect, however, very soon to be able to 
supplement our present work, wherever necessary. 
OVARIES OF GUINEA PIGS IN THE LAST STAGE OF PREGNANCY 
The condition of the ovaries of a guinea pig in the last days 
of pregnancy is as follows: there are small, medium sized and 
large follicles without degeneration of granulosa cells. In other 
large follicles various stages of granulosa degeneration are pre- 
sent. Many follicles show further advanced stages of atresia, 
in which connective tissue grows into the follicular cavity. 
Especially numerous are the last stages of atresia in which the 
zona pellucida is directly surrounded by very cellular connective 
tissue. Mitoses are seen in the granulosa cells of the well pre- 
served follicles. We also find here a few mature follicles which 
are characterized by an increase in cytoplasm of the granulosa 
cells. These follicles are large; their cavity is very wide. The 
nuclei of the granulosa cells are not as densely packed in these 
follicles as in the ordinary large follicles, this peculiarity being 
due to the marked development of the cytoplasm. They can 
be easily recognized in sections stained by haemotoxylin and eosin, 
inasmuch as they appear stained more reddish, in contradistinc- 
tion to the ordinary large follicles in which the blue color of the 
nuclei predominates, while in the mature follicles the red stain 
of the cytoplasm is a distinguishing feature. In these mature fol- 
licles the number of mitoses is very much smaller than in the 
ordinary large follicles. With the increase in the quantity of 
cytoplasm and the relative decrease in the nuclear material, 
