cleavage - major pattern of embryonic cell divison in which cytokinesis
completely separates cells during division; it is typically seen in
smaller eggs containing moderate (mesolecithal) to sparse (isolecithal)
yolk. Examples of eggs that divide holoblastically include those of
amphibians, mammals, non-vertebrate chordates, echinoderms, most molluscs,
annelids, flatworms, nematodes.