Amniotic fluid protects the foetus from

The function of the allantois in mammals is:

$A$: If both the ovaries are removed after the first trimester of pregnancy,still there would be normal growth of the foetus.
$R$: After the first trimester,the placenta secretes sufficient progesterone.

........ maintains the endometrium of the uterus.

Placenta has an outer layer which is selectively permeable and hormone secreting which is known as

Identical twins are