Visual abnormalities in albino wallabies: a brief note.

Abnormally reduced uncrossed retinofugal pathways and abnormally low retinal cell densities have been described in albinos of a number of species of eutherian mammal, but have not been studied in marsupials. The optic chiasm of marsupials differs from that of the eutherian brains that have been studied, with uncrossed fibres segregating from crossed fibres prechiasmatically in the marsupials, but not in the eutherians. We have examined the optic chiasm and the retina in albino and normally pigmented wallabies (Macropus rufogriseus) to determine whether the abnormalities found in eutherian albinos are also present in this marsupial. The uncrossed pathway of the albino wallaby is smaller than that of the pigmented animals and the cell density in the retinal ganglion cell layer is reduced at the area centralis. We conclude that the characteristic albino abnormalities are present in both groups of mammals in spite of the other known differences in the visual pathways. The albino mutation acts at the chiasm in a similar manner in both groups even though the determinants of the chiasmatic pathway differ.