In Part 3: How chordates got their chord, Marc Kirschner (Harvard Medical School) discusses how the overall body plan of vertebrates, arose from the invertebrates based on knowledge of the commonalities in their developmental mechanisms. Here again, the acorn worm, offers the key comparison, being close enough to us to share some recognizable features, but far enough away to indicate the direction from whence we came.

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...

Modern cell and developmental biology has a lot to contribute to our understanding of the deep history of animal origins, which until recently has been largely the province of paleontology. In this set of lectures, I hope to show how recent studies by a very small group of scientists on a virtually unknown phylum of marine organisms, the hemichordates, has helped explain some of the major mysteries of the origin of vertebrates. This is a tour of not only vertebrate origins but the...

Biology of chordates.