18 CARL G. HARTMAN 
just beginning to proliferate. Animal No. 343 had previously 
furnished bilaminar blastocysts (fig. 5, pl. 2) from the left 
uterus; she was killed seven hours and twenty minutes later and 
a litter of large blastocysts, still in the bilaminar stage, was 
removed (fig. 6, pl. 2): the interval allowed had been too short. 
Animal No. 346 (figs. 3 and 4, pl. 2) had yielded bilaminar blas- 
tocysts a little larger than No. 343 and an interval of nine hours 
and forty-five minutes had proved to be too long, for, when 
the animal was killed, the primitive streak was already well 
advanced in the second litter of ‘eggs. Profiting by these two 
experiments, when animal No. 353 appeared with large bilaminar 
blastocysts about the size of those in litter No. 346, a five and 
one-fourth hour interval proved to be the correct one, for the 
eggs in litter No. 353’ contain the first anlage of the primitive 
streak, one egg having as few as twenty-five mesodermal cells. 
In the operations I have found it most convenient to enter 
the abdomen through a short slit on one side of the pouch. 
For the sake of uniformity I select the left side as a matter of 
routine. The animal is shaved over this area and the incision 
is made as near the pouch as possible, care being taken not to 
cut through the pouch, especially in multiparae, which possess 
dilated pouches. The operated animal is bandaged; but it is 
impossible to keep the bandage on an animal unless the entire 
trunk is covered. I use over the bandage a jacket with holes 
cut for head and legs and tied over the back. As the animal 
usually sweats with the bandages on, the wound will heal better 
if they are removed at the end of three or four days. 
If, on opening the animal, the uteri are purplish and flaccid, 
the case is one of pseudopregancy and the organs may be left 
intact and the animal kept for another oestrus period, which 
takes place in about thirty days. If ovulation is recent, however, 
one uterus must be removed to ascertain the state of the eggs. 
If the appearance of the organs indicates that young stages are 
to be expected, the uterus is placed in warm Ringer’s solution 
and a slit is made through the musculature and peritoneum 
from one end to the other, and this must be done by a rapid 
manipulation of the scissors to precent eversion of the mucosa. 
