By the end of about .......... weeks,the body is covered with fine hair.

The eutherian placenta is derived from,or in mammals,the placenta is formed by:

The hormone relaxin,responsible for the easy birth of the baby,is secreted by . . . . . . .

What type of placenta is found in humans?

$A$ : 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.

The amnion of the mammalian embryo is derived from: