The development of the vascular system: a historical overview.

Development of the vascular system involves a complex sequence of inductive and differentiating signals leading to vasculogenesis and/or angiogenesis. Dissecting and exploring this process in its multifaceted morphological and molecular aspects has represented a basic contribution and a fascinating adventure in the history of biology. Vasculogenesis, that is de novo formation of vascular channels, initiates early during embryo development and prevails at the beginning of embryo patterning and organ formation. Angiogenesis, the process of shaping new vessels from preexisting blood vessels, mainly operates during postnatal life. In this historical introduction, we try to retrace the early steps of scientific speculation on vascular development and to recapitulate the principal paths leading to our present appreciation of blood vessel formation.