CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 63 
In other cases, however, such ova are surrounded by connective 
tissue. 
The connective tissue of the ovaries shows more differentiation 
at this period and is somewhat more fibrous. 
5. In ovaries of guinea pigs one to two months old the size of 
some of the follicles, in correspondence with the growth of the 
ovaries, enlarges. We see various stages of granulosa degenera- 
tion and of connective tissue atresia. Granulosa degeneration may 
take place in medium sized and in large follicles. In some ovaries 
the large majority of follicles may show either granulosa degen- 
eration or connective tissue atresia. Corpora lutea are not yet 
visible. 
6. Ovaries of guinea pigs three months old: Approximately at 
this period the ovaries have become mature. We find various 
stages of developing follicles and occasionally mature follicles 
ready to rupture. We find the various stages of granulosa degen- 
eration and of connective tissue atresia. We notice a greater differ- 
entiation in the structure of the stroma in different parts of the 
ovary. 
Corpora lutea, which occasionally are already in the beginning 
of degeneration, are present in some ovaries; in other animals 
ovulation has not yet taken place. 
It follows from these observations that degenerative processes 
in follicles set in approximately fourteen to eighteen days after 
birth, and ovulation and formation of corpoa lutea appear in 
guinea pigs two to three and a half months old. The ovaries and 
follicles must have reached a certain size, before ovulation sets 
in. The time required for the development of small into large 
follicles, with subsequent beginning of degenerative processes, is 
somewhat longer in the young growing animal than in the mature 
guinea pig, but in both the periods of time are of a similar order 
(approximately nine and fourteen days respectively). —* 
