If the egg is not fertilized, the lining of the uterus begin to pull away with the unfertilized egg.
if
the egg is not fertilized in the days following its passage through the
tube, the progesterone begins, too, to fall. The unfertilized egg
eventually dissolve and the uterine wall surplus stands. The assembly is
then discharged as "blood" to the outside, through the cervix and vagina.
