Reason for crossed projections in the nervous system?

[Kalman Rubinson]

@ucl.ac.uk wrote:
: A hypothesis I came across last night, attributed to Marcel Kinsbourne by 
: Steven Pinker in his book "Language as Instinct", runs as follows: 
: bilaterally symmetrical invertebrates have an uncrossed nervous system, 
: their spinal cords (or the invert. equivalent) ventrally and their hearts 
: etc. dorsally, whereas vertebrates have a crossed nervous system, their 
: spinal cords dorsally and their internal organs ventrally. Kinsbourne 
: speculates that sometime during invert-vert evolution, the head was 
: twisted around 180 degrees so that it points the other way (sort of like 
: what happened to flatfish only worse). I thought that was a kind of cute 
: idea. I have no idea whether it has any merit or not. 

That makes the assumption that there is a direct lineage between the two 
which I regard as unlikely.

Kal