The pattern of rhabdomeres is disrupted in hemizygous males and homozygous females, with rhabdomeres from neighbouring photoreceptor cells often fusing to form a ring. The fusion is limited to the external rhabdomere membrane in hemizygous males, and the degree of fusion within each ommatidium varies from no fusion, through to fusion of all the rhabdomeres into a ring. All degrees of the fusion phenotype are visible at eclosion. The ommatidia of homozygous females all show the extreme fusion phenotype. The rhabdomeres do not extend the length of the retina, in contrast to wild-type, but are restricted to the distal region. This shortening of the rhabdomeres is distributed evenly across the retina. A decrease in the density of axonal projections is seen both between the retina and the lamina and between the lamina and the medulla. The optic lobe appears less densely organised than normal. The penetrance of a deep mutant pseudopupil phenotype is cold sensitive; at 17^oC the penetrance is 92%, at 29^oC it is 65%. fur¹ mutant photoreceptors have reduced sensitivity to light of all wavelengths compared to wild-type, and lack a prolonged depolarising afterpotential. The eyes of 40 and 60 hour pupae appear normal.