The blastula (from Greek βλαστός (blastos), meaning "sprout")'s an early stage of embryonic development in animals. It's also called blastosphere. It's produced by cleavage of a fertilized ovum and consists of a spherical layer of around 128 cells with a large fluid filled space called the blastocoel in the animal pole of the embryo. The blastula follows the morula and precedes the gastrula in the developmental sequence. Research A whitefish blastula's often… (More on Blastula)