CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 53 
which would perhaps agree with an opinion expressed by Regaud 
and Dubreuil,’ is correct. 
The second generation of corpora lutea is represented by small 
vacuolar bodies with relatively much connective tissue and thick 
vessels. These atretic corpora lutea originated at the time of the 
second last ovulation and are therefore approximately thirty-three 
to forty days old. If this second last ovulation had been followed 
by pregnancy, the corpora lutea of this period are still much larger 
than the corpora lutea of the corresponding generation without 
an accompanying pregnancy ; but a considerable shrinking of these 
corpora lutea has also taken place. The vessels are to a great 
extent collapsed. The lutein cells are finely or coarsely vacuolar, 
take less stain, still possess nuclei and a distinct cell wall, 
staining with eosin. The third generation of corpora lutea is 
again represented by yellow bodies. They are not present in all 
ovaries, but are found especially in the ovaries of older guinea 
pigs. Occasionally the degenerating corpora lutea of the second 
generation may also be absent. 
In guinea pigs in which the last ovulation was followed by preg- 
nancy, the condition of the follicles is very similar. The corpora 
lutea of the first generation, however, are large and show frequent 
mitoses in lutein cells, occasionally also in lutein cells the peri- 
phery of which is vacuolar. There are possibly also mitoses pres- 
ent in the endothelial cells. The retrogressing corpora lutea of 
the second and third generations are in pregnant animals of a 
similar character as those described in the ovaries of guinea pigs 
of the same period without an accompanying pregnancy. 
OVARIES OF GUINEA PIGS FIFTEEN TO NINETEEN DAYS AFTER 
OVULATION 
Pregnancy had in most cases been prevented by the same means 
which were used in the preceding stages. In a few instances in 
which pregnancy had occurred an early abortion followed. The 
follicles exhibit on the whole the same character as in the preced- 
ing stage; we find good follicles of small, medium and large size, 
3C. R. Soc. Biol., 54. 1908. 
