Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. lI

DISCUSSION

PODLIACHOUK L., and VANDEPLASSCHE M. Observations made on chorial
membranes from about 50 cases of dizygotic twin pregnancy in the mare
have shown that nearly all cases are bicornual and that invagination
of the chorial sacs develops in about 75 %. Tissular fusion was
observed from the fifth month on in about 40 %. Macroscopic vascular
anastomosis between both fetal placentae was shown in 5 out of 27
cases. Blood groups in the parents and foals of 10 cases of twin-
pregnancy have been determined, using 18 referenceantibodies. Identical
blood groups were found in both foals of 5 cases of twin gestation,
indicating chimerism and bloodanastomosis between both chorions ;

blood chimerism was probable in 2 other cases in which one foal only
could be examined. Macroscopic fusion between both chorial sacs may
occur without the establishment of vascular anastomosis, and blood-
chimerism has been shown in some cases where both chorial sacs seemed
to be free, thus indicating the occurence of rather microscopical
bloodanastomosis. Different blood groups occured in three cases of twin
pregnancy. That makes alltogether a surprisingly high incidence of vas-
cular anastomosis between the chorial sacs in cases of bicornual twin-
gestation. In two cases of dead-born and three cases of living bisexual
twins at one to two years age, the genital apparatus of the female
co-twin was found to be normal. Those observations point to a much
lower incidence of freemartin-deformation than in cattle.

871