He LEO LOEB 
In this series of animals pregnancy had been prevented after 
a preceding copulation, either by ligaturing the tubes within the 
first two days after copulation, or by making long incisions into 
the uterus approximately four to six days after copulation. 
The ovaries were also examined in a certain number of other 
guinea pigs of this period in which pregnancy existed. The accom- 
panying pregnancy does not produce any marked change in the 
ovaries and the preceding description applies on the whole equally 
well to these ovaries. 
OVARIES OF GUINEA PIGS THIRTEEN TO FIFTEEN DAYS AFTER 
OVULATION 
In this series of animals pregnancy was prevented in the same 
manner as in the series of animals examined ten to eleven days 
after ovulation. The follicles have approximately the same 
character as in the previous period. We see the same varieties 
of follicles. Small follicles grow and become large and, after 
having reached this stage, or even at a slightly earlier stage, 
granulosa degeneration sets in with consecutive connective tissue 
atresia. In the granulosa of well preserved follicles numerous 
mitoses are present, and mitoses may even be found, if a slight 
amount of granulosa degeneration has taken place. The corpora 
lutea of the last ovulation (I generation) show more generally the 
beginning of vacuolization, especially in the periphery of the 
corpus luteum; but on the whole the corpus luteum is still well 
preserved and usually mitoses are found in some of the lutein 
and occasionally in cells belonging to blood vessels. 
In the center we find connective tissue with thin spindle-shaped 
nuclei, and a number of vessels with walls consisting of several 
rows of cells penetrate into the central connective tissue. In 
some of the lutein cells the protoplasm appears dense and stains 
deeply with eosin. It appears probable that in such cells the nuc- 
leus had started to divide by mitosis, but degenerative processes 
seem to have set in and interrupted the process of the mitotic 
division. We are however not certain that this interpretation, 
