The amount of yolk determines the type of cleavage in the egg. In supperfecial meroblastic cleavage, the cleavage remains restricted to the peripheral portion of the egg. This cleavage occurs in arthropods especialy insects. In birds and reptiles discoidal meroblastic cleavage occurs where, divisions are confined to the cytoplasmic disc at animal pole. In mammals, holoblastic cleavage occurs ie, division of whole egg and not a part.