Birdie:
Regarding the eye argument bringing up the insect argument is heading in the wrong direction. They come from a completely different branch of the evolutionary tree. They parted from our line when our ancestors began the embryonic development of the digestive tract with the anus while theirs started with the mouth.
If you want an example of the earliest steps in the progress from the most primitive chordates toward the vertebrate there is no better example then the hagfish.
These creatures have no fins, eyes incapable of forming an image because it has no with no lense, no jaw, teeth made of keratin, only a partial cartilage skull with a fibrous sheath around the brain.
They even absorb food through their skin.
http://en.wikipedia.org/wiki/Hagfish