In Part 2: Telling the back from the front or what the chordates invented, Marc Kirschner (Harvard Medical School) discusses why we look like invertebrate animals turned upside down, i.e. vertebrates have their central nervous system on their backs and invertebrates have it on their bellies.

Nicole Le Douarin shares her research on the role of the neural crest in skeletal development. The Q/C (quail/chick) marker system revealed that apart from the peripheral nervous system (PNS), the melanocytes and some endocrine tissues, the NC plays a major role in the construction of the vertebrate head. The entire facial skeleton and part of the skull (frontal, squamosal, parietal bones) are of NC origin together with the connective tissues of the face and ventral part of the neck. The...