Homologues of developmentally important regulatory genes from other species have been found to be expressed in early amphibian development. The Drosophila dorso-ventral polarity .gene, dorsal, is involved in the formation of ventral structures and dorsal- mutants arise from a default state where only dorsal structures are formed. A Xenopus homologue of dorsal may play a crucial role in interpreting some of the earliest embryonic signals