Handbuch der vergleichenden und experimentellen entwicklungslehre der wirbeltiere : bd. 1, teil 1, hälfte 2
According to the preface to this volume, there are probably as many views about the initial formation of the vessels and blood as researchers have expressed themselves on this subject, which in any case proves that this is one of the most difficult matters. Thus, after looking at the literature, the authors needed their own investigations.