How many cleavages are required to form a $16$-celled blastomere?

The embryo with $8-16$ cells is called ........

Relaxin (a hormone) is secreted by

Human placenta is called haemochorial because . . . . . . .

Which extraembryonic membrane in humans prevents desiccation of the embryo inside the uterus?

$A$ : 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.