The foetal membrane which is the source of first blood corpuscle to enter the circulation of the embryo is called

$A$ : Leydig’s cells synthesise and secrete testicular hormones called androgens.
$R$ : Leydig’s cells are located between the Sertoli cells.

The animals in which complete embryo develops in the mother's body through placenta are

Which one of the following is the incorrect match of the events occurring during menstrual cycle?

Number of sperms present in a single ejaculation of semen contains

Test tube baby means a baby born when