CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 61 
without contact with males, and subsequently further ovulations 
occurred. Under such conditions the successive ovulations do 
however not occur in the same intervals in all animals; in some 
cases a delay in ovulation may take place: this accords well with 
our previous observations. The conditions of the follicles corre- 
spond to the time elapsed since the last ovulation, as indicated 
by the state of the corpora lutea. 
Not in every case however does a spontaneous ovulation take 
place without contact with male. In several cases neither new 
nor retrogressing corpora lutea could be found ia the ovaries of 
guinea pigs which, according to their age, ought to have ovulated, 
but in which no sign of heat had been noticed during an observa- 
tion extending over a certain period of time. In other guinea pigs 
which had been in heat recently, but in which copulation had 
been prevented, no new ovulation corresponding to the period of 
heat had taken place at the time of examination. 
SOME OBSERVATIONS ON THE POSTFETAL DEVELOPMENT OF THE 
OVARY OF THE GUINEA PIG 
In connection with the cyclic changes in the adult ovary of the 
guinea pig, just described, we thought it of interest to determine 
the time at which these cyclic changes set in. For this purpose we 
studied a series of ovaries at differents stages of the growing guinea 
pig. 
1. Jn the ovaries of a fetus near the tume of birth many follicles 
are present in the cortex. These follicles have not yet a cavity 
and the largest follicles have a granulosa consisting of three, or four 
rows of granulosa cells; in the latter some mitoses can be seen. 
No distinct differentiation appears in the connective tissue of the 
different parts of the ovary. 
2. In the ovaries of guinea pigs four, five and seven days old 
we find a cavity in a certain number of the follicles; no atretic 
processes have as yet taken place. The theca interna cells are 
distinguished from the surrounding connective tissue through the 
