60 LEO LOEB 
few mitoses which were found especially in the discus proligerus. 
Some of the nuclei of the granulosa cells appeared somewhat con- 
tracted in these follicles, but no marked degeneration of the gran- 
ulosa cells was found. 
The corpora lutea of pregnancy were large, the cytoplasm of 
the lutein cells stained red yellow with eosin; the cell outlines 
were quite distinct. The large majority of the lutein cells were 
compact and did not show vacuoles; the nuclei were vesicular. 
A few mitoses were found in lutein cells. Only very little con- 
nective tissue was present in the center of the corpora lutea. 
Some of the vessels had thick walls, while other vessels were of a 
capillary character and had either a wide or narrowlumen. We 
see therefore that also at later stages of pregnancy the follicles 
continue to grow and to degenerate, and that even at this period 
of pregnancy follicles may mature. The lutein cells of the corpora 
lutea of pregnancy continue to show mitotic nuclear figures and 
well preserved cytoplasm at a time when, in the ordinary corpora 
lutea, retrogression is very far advanced. 
OVARIES OF GUINEA PIGS IN WHICH COPULATION HAD BEEN 
PREVENTED 
A large number of ovaries were examined of female guinea pigs 
which had been kept separated from males for various lengths of 
time. 
One set of guinea pigs was separated from males before sexual 
maturity had been reached. The ovaries were examined, when the 
animals were six and twelve months old. In every instance ovu- 
lation had taken place repeatedly and we usually found the three 
generations of corpora lutea which we described in the case of 
guinea pigs which had copulated, namely relatively young cor- 
pora lutea, retrogressing vacuolar corpora lutea and _atretic 
yellow bodies. 
In another series guinea pigs were guarded against contact 
with males after delivery, and were kept separated from males 
for various periods of time. In this case a spontaneous ovulation 
took place after delivery, at least in the majority of cases, even 
