38 LEO LOEB 
ries of which he examined. He also seems to have examined a 
relatively very limited number of ovaries of animals during the 
different stages of pregnancy, and furthermore he studied only 
certain parts of each ovary. A methodical study of ovaries of 
non-pregnant animals was not undertaken. While his obser- 
vation that after copulation all follicles become atretic is ap- 
proximately, but not altogether correct, as far as its general 
validity is concerned, in the guinea pig the processes taking place 
in the ovaries during the subsequent stages differ from the con- 
ditions described by Stratz in the case of Tupaja, Sorex and 
Tarsius. 
Furthermore Stratz does not recognize the essential factor 
upon which the cyclic changes in the ovaries depend. The con- 
clusions in the last chapter of his publication show this clearly. 
He summarizes as follows: If we find all follicles atretic, the 
animal has been pregnant. If at the same time a new corpus 
luteum is present, we have to deal with an early stage of preg- 
nancy. If we detect some normal follicles, besides numerous 
atretic follicles and a new corpus luteum, we have to consider a 
puerperal condition of the animal. A large number of atretic 
besides a few normal follicles also suggests a puerperal state. 
These general conclusions are not justified; the changes of 
the follicles do not, as Stratz assumes, depend upon pregnancy, 
and if we should attempt to use the criteria given by Stratz in 
the case of guinea pigs and mammals in general we would be 
liable frequently to make mistaken diagnoses. Notwithstanding, 
these necessary criticisms, the work of Stratz is very valuable 
and it advanced to a considerable extent our knowledge of the 
ovaries. 
Since his publication no more detailed investigation into the 
processes taking place in the ovaries under various conditions 
has appeared, as far as we are aware. Within recent years, how- 
ever, the question has been raised whether a new ovulation can 
take place during pregnancy. 
We limited our investigations to the study of the ovary of the 
guinea pig. We examined several hundred pairs of ovaries of 
animals in which the period of the sexual cycle at which the ovaries 
