THE ORIGIN AND EARLY EVOLUTION OF METAZOA NS

Metazoans appeared 800 million to one billion years ago by derivation from preexisting unicellular organisms which most probably were flagel lates. Several transitional steps are proposed in the paper to explain the evolution from unicellular to pluricellular animals. Specifically , it is argued that the earliest metazoans arose not by aggregation of solitary cells, but by scission of plurinucleated cells.