CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 41 
on account of the previous proliferation of lutein cells which en- 
croached more and more upon the space originally filled by the 
connective tissue. The corpora lutea are large. The lutein cells 
show signs of degeneration; they are finely vacuolar and may have 
a foamy appearance; a certain number of cells take less eosin and 
appear therefore pale. Many cells have a sharply defined, red- 
staining outline. The nuclei also show changes; they are frequent- 
quently deformed, indentated; or they are round, vesicular, but 
stain less with haematoxylin; they appear somewhat karyolytic. 
Mitoses could not be seen in the lutein cells. The degree of retro- 
gressive changes may vary in different corpora lutea even in the 
same ovary. 
We see therefore that even before delivery and before a new 
ovulation has taken place, degenerative changes set in in the cor- 
pora lutea, and it accords with these retrogressive changes that 
mitoses are absent or at least very rare in such corpora lutea. 
Besides these corpora lutea of pregnancy we may find in such 
ovaries ‘yellow bodies’ representing the last stage of retrogression 
of corpora lutea. In thecorpora lutea which were transformed into 
such yellow bodies, degeneration must have set in approximately 
sixty to sixty-five days ago. These ‘yellow bodies’ have the fol- 
lowing structure: In their centre and periphery we find hyaline 
connective tissue; between these two zones of hyaline connective 
tissue a relatively small number of degenerated large lutein cells 
is enclosed, in which, during the process of retrogression, a large 
amount of yellow pigment was produced. 
OVARIES OF GUINEA PIGS WITHIN TWO DAYS AFTER DELIVERY 
In the period directly following delivery the condition of the 
ovaries, as far as follicles and corpora lutea are concerned, is 
approximately the same as in the period preceding it. The growth 
and degeneration of the follicles still continue to take place, and 
in follicles in which the granulosa has completely or almost com- 
pletely degenerated an ingrowth of connective tissue and complete 
atresia of the follicles occur. The retrogressive changes in the 
corpora lutea also progress, but at a slow rate, and on the whole the 
JOURNAU OF MORPHOLOGY, VOL. 22, NO. 1 
