Figure 38.7: Some Patterns of Cleavage Differences in patterns of early embryonic development reflect differences in egg cytoplasm. (A) The frog is a model organism representing complete cleavage. (B) Zebrafish embryos illustrate incomplete cleavage, in which the large yolk mass limits the planes of cleavage. (C) Fruit flies have another type of incomplete cleavage. Nuclear staining reveals the syncytial nuclei characteristic of their early development. These nuclei migrate to the periphery of the egg. Cleavage furrows then move inward to separate the nuclei into individual cells.