Advancing cleavages of the frog’s fertilised egg produces an embryonic stage, with a fluid filled cavity called as Blastula. The cavity of blastula is called as blastocoel, which is filled with an albuminous fluid called as Blastocoel jelly. The presence of cavity in blastula distinguishes it as a coeloblastula. Blastula is more or less spherical in shape.

Blastocoel is covered by upper layers of small, black, pigmented micromeres and its floor is more or less flat and formed of non- pigmented large micromeres. Micromeres and micromeres constitute the blastomeres which arrange to form a true epithelium called Blastoderm. In animal pole, blastoderm is Q- cell thick and in vegetal pole it has many cell thicknesses. The presence of yolk makes the blastocoel eccentric. Blastula consists of many cells which are bought into their portion during cleavage. It later gets transformed to gastrula through gastrulation.