The vegetal hemisphere of an egg consists of:

$A$: In frog,a gray crescent is formed during fertilization.
$R$: It is because the black pigment granules move away from the point of entry of the sperm in the animal half.

If the ectoderm from the neural tissue area is removed from the embryo and transplanted in place of the presumptive belly ectoderm,the embryo will develop:

Grey crescent is present in

In which of the following animals is cleavage restricted to a small portion of the animal pole of the egg?

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