In macro and telolecithal eggs site of amphimixis lies in the

Archenteron is formed during

In female mammals Bartholin's glands open into the

$A$ : Corticotrophin releasing hormone is a part of the clock that establishes the timing of birth.
$R$ : The signals for parturition originate from the fully developed foetus and placenta which induce mild uterine contractions called foetal ejection reflex.

Inhibition of uterine contraction ceases and the bleeding and cramps of menstruation begin due to