Which of the following drugs inhibits metamorphosis in frogs?

The jelly layer of a frog's egg is:

What does the completion of the formation of the archenteron indicate?

The structure which remains unchanged during the metamorphosis of a frog's tadpole is:

During embryonic development,the establishment of polarity such as anterior/posterior,dorsal/ventral,and medial/lateral axes is called:

The $Gray \text{ } Crescent$ is an area in the egg that is: