The type of cleavage found in mammals is:

Where is the chorion found?

The hormone responsible for the implantation of the embryo in the uterus and the formation of the placenta is:

Which is the correct sequence in the development of man?

$A$ : 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.

Sometimes the separation of twins is incomplete and they are born attached and remain so even after birth. Such twins are known as: