[adrian_b]

TFA is about the fact that originally the vertebrates had at least 3 eyes, 2 lateral eyes and 1 median eye (pointing upwards towards the sky, in the middle of the head).

Most vertebrates, with the exception of a few species, like tuatara, have lost the middle eye.

The subject of the parent article is that it was expected that if the third eye was lost, the retinas of the 2 lateral eyes that have been preserved are derived from the retinas of the 2 ancient lateral eyes, but despite this expectation, the retinas of the modern lateral eyes of the vertebrates are derived from the retina of the ancient middle eye.