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

The diagram shows one of the human embryonic developmental stages. What do $A$ and $B$ indicate?

Corpus luteum is the source of secretion of

The respiratory function of the embryo is performed by

Which hormone is produced only in the female body during pregnancy by the placenta?