The mother germ cells are transformed into a mature follicle through series of steps. Provide the missing steps in the blank boxes.

$\boxed{{\text{Oogonia}}}$ $\to $ $\boxed{\text{A}}$ $\to $ $\boxed{{\text{Primary follicle}}}$ $\to $ $\boxed{\text{B}}$ $\to $$\boxed{\text{C}}$ $\to $ $\boxed{{\text{Mature or Graafian follicle}}}$

In human female, the blastocyst

Which one of the following parts serves the function of primary organizer in frog

The type of blastula formed in birds is

In a simplest type of placenta the foetal blood is separated from the maternal blood by six barriers. How many barriers are lost in human placenta

Fertilizin is a chemical substance produced from