In a human foetus,the limbs and digits develop after:

The function of the allantois in mammals is:

$A$: Blastocyst undergoes gastrulation to produce the three germinal layers.
$R$: This involves cell movements (morphogenetic movement) that eventually help to attain new shape and morphology of embryo.

Select the odd one out.

During embryogenesis,the zygote undergoes:

Explain the difference between the following terms:
$(1)$ Menstrual flow - Menstrual cycle
$(2)$ Embryo - Foetus