The egg undergoes cleavage and forms:

By the end of the second month of pregnancy,the foetus develops........

The substance secreted by the corpus luteum is

In human beings,at the end of $12$ weeks (first trimester) of pregnancy,which of the following is observed?

Major features of embryonic development at various months of pregnancy are given below. Choose the correct option for the correct sequential events.
$(i)$ The first movements of the foetus
$(II)$ The foetus develops limbs and digits
$(III)$ The embryo's heart is formed
$(IV)$ The body is covered with fine hairs

The mammalian primitive streak gives rise to