Microvillar Orientation in the Retina of a Pierid Butterfly

Abstract

The orientation of microvilli in the compound eye of the butterfly. Pieris protodice, has been examined using electron microscopy. The retinula cells comprising each ommatidium have been divided into four types based upon microvillar orientation, position of nucleus, and location within the om­matidium. The vertical and horizontal retinular types have microvilli in the distal one-third to half of the retina. There is alteration in the orientation of these microvilli of up to 90 . The rhabdom is dominated by the microvilli of the diagonal retinulae in the proximal retina. There is consistant orientation of the diagonal cell microvilli throughout the retina. In mid-retina, these microvilli undergo dramatic alteration in length, leading to a Crustacean-like organiza­tion. for some 50 μm. The basal, or eccentric, retinula cell is bilobed. and has only a few microvilli projecting a short distance into the rhabdom.