The gastrula stage is characterized by which of the following?

$A$ : The morula passes through the phase of compaction,producing two major types of cells: the peripheral cells and the inner cell mass.
$R$ : The descendants of the inner cell mass become the trophoblast cells.

During pregnancy,the levels of which hormones are increased?

The process by which primary germinal layers are formed is called

$A$: 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.

Where does the development of the zygote take place in viviparous organisms?