Twin Placentation - 75 Days.
The amniotic sacs have been injected with methylene blue to better illustrate their size. Notice the sharing of the chorioallantois and some of its circulation. The latter leads to freemartinism in the female fetus that is co-twin to a male fetus. Notice also the normal (common) necrotic tip of the left extremity of the membranes.
Drost M (1978)