26 CARL G. HARTMAN 
the same condition that prevents the onset of oestrus. On the 
other hand, operated animals recover quickly, often eating 
heartily several hours after the operation. Their wounds heal 
readily and the animal comes into heat again even after two 
operations and after double hysterectomy, in the same manner 
as if the abdomen had not been opened. Certainly, if Bischoff 
a century ago was able to secure as many as six different stages 
of normal embryos from one rabbit, without anesthesia or 
asepsis, successively opening the abdomen and ligating off 
segments of the uterine horns ‘‘until inflammation set in,” then. 
a very simple operation on the opossum under modern surgical 
precautions should have no deleterious influence on the embryos. 
If, now, to test the matter further, we compare the proportion 
of normal’ eggs secured at the first operation (table 1 above) 
with the proportion from the second operation, we find 63.1 
per cent normal (item 3, table 1) for the former and for the 
latter 67.4 per cent (items 4 and 5, table 1), an unexpectedly 
but quite accidentally large percentage of normality for the 
operated animals. 
These figures, however, include under ‘abnormal’ all unfer- 
tilized eggs, which should be left out of consideration, since we 
are here testing the effect on the development of the eggs and 
embryos. We must, therefore, count only the dead and de- 
fective fertilized eggs in given litters, selecting comparable 
. stages. Table 2 gives this data for bilaminar vesicles of litters 
in which every egg was studied; and cases from the second 
operation are selected in which at least one day had intervened 
after the first operation. Table 3 gives similar data for primi- 
tive-streak stages up to 5 mm. in diameter. The litters are 
arranged more or less in order of relative stage of advancement. 
From a study of tables 2 and 3 it is apparent that there is a 
high rate of mortality in the eggs of the opossum, both of 
operated and unoperated animals, but that wholly normal 
litters occur in both classes. Some cases are of special interest. 
No. 334, for example, yielded a perfect litter of eggs from the . 
left uterus, but only a single abnormal vesicle 20 hours later 
from the right uterus. On the other hand, No. 344 yielded 7 
