Résumé
Ascidian embryos were the first animal embryos to be experimentally manipulated by Man at the end of the 19 century. The mosaic theory of development was born from these experiments and thosecarried out by Conklin 20 years later. These astonishing animals, some of which are eaten as delicacies in France and other countries, belong to the tunicates, which are the only animals to produce cellulose. They are, however, the closest living relatives to the vertebrates. Neglected throughout most of the 20(th) century, ascidians have recently come back in the limelight in the wake of the sequencing of the genomes of Ciona intestinalis and Ciona savignyi. These small, unduplicated genomes harbour 16 000 to 20 000 genes and are 20 times smaller than the human genome. Ciono eggs can be microinjected and easily electroporated, which make this system suitable for the study of developmental gene regulatory networks.