References
Martindale MQ. The evolution of metazoan axial properties. Nat Rev Genet. 2005 Dec;6(12):917-27. PMID: 16341072
Pires-daSilva A, Sommer RJ. The evolution of signalling pathways in animal development. Nat Rev Genet. 2003 Jan ;4(1):39-49. PMID : 12509752