Abstract In-vivo imaging of the development of complex retinotectal axon arbors indicates that arbors branches can form and extend in the absence of growth cones. A variety of imaging protocols were used to observe arbor elaboration over a range of time intervals and total observation periods. Growth cones are observed relatively rarely in the growing axon arbors. Branch addition, or backbranching, and branch extension occur without apparent specializations at growing branchtips. Branch addition within the elaborating axon arbor is discussed with respect to the process of interstitial branching of axon collaterals.