In fact they die soon after birth, they have no eyes or nasal cavities, olfactory bulbs fail to develop and there are a few other defects in the brain. It is thought that the original eyeless mutation in Drosophila arose through the insertion of a transposable element into an eye specific enhancer. The ectoderm which becomes the cornea also expressses Pax-6. It is also expressed in the nasal epithelium a few days later. This induced the expression of ectopic eyes.
Picture shows the facets induced on the leg.
Ectopic eye expression was induced wings in all of the 6 legs, the antennae, and the halteres. The best developed of these ectopic eyes were observed on structures that had derived from the antennal and wing discs. The facets of the ommatidia , were occasionally fused and irregularly spaced, but distinct ommatidia, bristles, and lenses were observed. It is not known however whether the axons of the photoreceptors in these eyes directly innervate the correct area of the brain, but they have been shown to be electrically stimulated by light. The overhead also shows an ectopic eye in Drosophila whose expression was induced by the mouse homologue of Pax-6, Sey , as can be seen the induced eye is of the ommatidal Drosophila type rather than the mouse simple eye type.