The origin of Metazoa and Weismann's germ line theory.

Weismann's theory asserts that the continuity of germ cells throughout the entire life cycle is insured by the protection of the somatic cells which represent a distinct lineage. On the basis of embryological data and the organization pattern displayed by some highly differentiated unicellular organisms, it is postulated that the soma of multicellular animals has probably arisen as an accessory structure for an initially unicellular system.

PMID: 2665023 [PubMed - indexed for MEDLINE]