70 LEO LOEB 
after delivery had taken place. From ten to twelve days after 
delivery yellow pigment was seen in a few of the lutein cells in the 
corpus luteum of the previous pregnancy. 
Thirteen to twenty days after delivery the corpus luteum is still 
much larger than an ordinary corpus luteum at the same period 
after ovulation, but considerable shrinking has already taken 
place. Twenty-seven days after delivery the corpus luteum is 
very small and vacuolar, with much hyaline connective tissue, 
but has not yet been transformed into a yellow body; but at a 
later stage, approximately sixty days after delivery (or possibly 
somewhat earlier) the corpus luteum appears as a yellow body, 
and as such it may persist for some time. 
d. In the developing ovaries degeneration of the granulosa and 
connective tissue atresia of follicles are found as soon as the folli- 
cles have reached a relatively large size; these retrogressive changes 
first appear in guinea pigs approximately fourteen to eighteen 
days old, while the first ovulation appears much later, namely 
two to three and a half months after birth. 
