Final answer:
During the early part of the cleavage stage in frog development, the rapidly developing cells divide without increasing in size. After cleavage, the cells rearrange themselves to form a hollow ball called the blastula.
Step-by-step explanation:
During the early part of the cleavage stage in frog development, the rapidly developing cells undergo a process called cleavage, where they divide without increasing in size. This means that the cells divide rapidly but without an increase in mass. After cleavage, the cells rearrange themselves to form a hollow ball with a fluid-filled or yolk-filled cavity called the blastula.