In this study the sequence of vascular reorganization of the vascular network after partial section of a branch of the left chorioallantoic artery is described in the chick embryo chorioallantoic membrane. After several house (24-72), the defect of the artery is consistently bypassed by a collateral interconnecting of the stumps of the damaged vessel in such a way as to re-establish its continuity, according to a precise scheme which was similar in all cases that underwent the same type of ablation.