Pax6 Is a Transcription Factor Noted for Its Unique Role

Pax6 is a transcription factor noted for its unique role in specifying eye development across the animal kingdom. A homologous gene known as eyeless specifies eyes in Drosophila, and misexpression of mouse Pax6 can cause ectopic eyes in flies! This creates a quandary -- how can we explain the universality of the master regulatory gene for eye development, with the striking variability of eye anatomy in different phyla?
-Misexpression of the Pax6 gene was shown to promote eye development in both vertebrates and invertebrates. The authors of this study suggested that this was evidence that eyes evolved only once. What other evidence contradicts this view?

A) Invertebrates normally have only simple eyespots.
B) Many different transcription factors can initiate eye development when misexpressed.
C) While the anatomy of all animal eyes is the same, lens proteins vary greatly.
D) The anatomical structure of insect, mollusk, and vertebrate eyes are quite different.