robable that among segmented organisms reduction is the essential evolutionary mechanism, as the evidence implies, and that simple chordates are like vertebrate embryos because they are vertebrate embryos; the rest of their ontogeny has been lost (Lundberg, 1995, www.noevalley.com/segment/trad.htm).
The study of the development of the nervous system depends in large part on research into the different nervous systems among animal groups today. This process is explained by Anderson (1997), who is conducting such research in Santa Barbara:
The basic philosophy that governs our research is that, although ion channels in something like a jellyfish may be slightly different functionally from the equivalent channel in a vertebrate, the structures of the two are remarkably similar, despite the 500 700 million years of evolution that have separated the two groups. Our approach is to let the evolutionary history of a particular ion channel tell us something about the structure of that channel. For instance, in the case of an ion channel that lacks a pa
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