Enrique wrote:
>> George Hammond wrote:
> >
> > Richard L. Hall wrote:
> > >
> > > How many vertebrates lack eye lenses? Fish have them as do all
> > > tetrapods that I know of. So maybe the answer is zero. There are
> > > some species that have greatly reduced eyes and presumably greatly
> > > reduced optic tracts. Still, so many other central systems
> > > decussate, that it seems unlikely that something like the formation
> > > of a lens could account for crossed visual pathways.
> >
> > [Hammond]
> > So far as I know, animals that can see but without lenses,
> > e.g. "compound eyes", have ipsilateral CNS structure...
> > there is no decussation... further support for the theory.
> > Take a fruit fly for instance.
> >
>> This only means that there is a significant difference in
> design between a fly eye and a vertebrate eye (and brains!).
> Each little facet in a compound eye do have a lens. I think
> the point is, probably, that compound eyes are not imaging
> devices, but light detection devices.
GH: Iyuh, iyuh
>> As others has posted before, a pinhole will produce an
> inverted image. So, evolving a whole lens-ed eye from a
> primitive pinhole/retina projection eye will not imply a
> sudden image inversion when the lens come to function.
GH: Who said it was a pinhole, Sadie Hawkins? More likely
it was just a light receptive surface.
>> The decussation of CNS connections was probably a completely
> independent event in the evolution of the antecessors of
> vertebrates. Once taken, almost impossible to go back.
GH: Really
>> Enrique
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George Hammond, M.S. Physics
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Website: http://people.ne.mediaone.net/ghammond/index.html
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