A large number of experiments have been devoted to the study of the generation and development of the high-frequency structures, i.e. the chain of ring-like vortices and breakdown of the chain of ring-like vortices, to the investi-gation of their relevance to laminar-turbulent transition in a boundary layerow; however, the origins of turbulence via the process of ow randomization are still not well understood. For this reason a detailed experiment was performed to document the important shape and con guration of the late-stage transitional structures and to investigate some of the still insu