The graafian follicle now ruptures to release the secondary oocyte (Ovum) from the ovary by the process called

How many sperms are formed by four primary spermatocytes?

If both ovaries are removed from pregnant human female in first trimester of pregnancy then it will lead to

Human placenta is derived from

Fluid filled cavity called $...A...$ is developed in $...B...$ follicle called $...C....$ Here $A, B$ and $\mathrm{C}$ are

Extra embryonic membrane amnion is not found in amphibians because