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

The embryonic body form stage is characterized by:

The first sign of the growing foetus may be noticed by listening to the heart sound carefully through the stethoscope. The embryo's heart is formed . . . . . . .

Archenteron is formed during

Following changes can be seen in the first trimester of pregnancy,$EXCEPT$:

$A$ : 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.