Cattle were injected with PMS, bred and slaughtered 3, 30, 45, 60 and 90 days after ovulation and the genital tracts dissected. From 30 to 90 days of pregnancy the percentage increase in the weight of single embryos was 85 times as much as the increase in crown-rump length. The volume of amniotic fluid increased 580 times in the second month of pregnancy and increased twice during the third month of pregnancy. The allantochorion did not lengthen between 60 and 90 days of pregnancy. At 30 days of pregnancy there was no significant difference in the crown-rump length or the weight of embryos of singles, twins, triplets, quadruplets or quintuplets. The volume of placental fluid per embryo was higher in singles than in twins and triplets; the volume of placental fluids per embryo decreased further in quadruplets and quintuplets. The weight of the placental membranes per embryo was heavier in singles than in twins, triplets and quadruplets; the weight of membranes was markedly decreased in quintuplets. The effects of overcrowding in utero on the conceptus was more pronounced at 60 days than at 30 days and in quintuplets than in triplets and quadruplets. Anastomosis of vascular supply of allantochorions occurred as early as 30 days of pregnancy.