Cell movement on light adaptation in the retina of Lethocerus (Belostomatidae, Hemiptera)

Abstract

1. The ommatidial structure of a giant water bug (Lethocerus, Belostomatidae) is described, as well as the cell movements that occur on light/dark adaptation. 2. Four cone cells beneath each facet connect the thick cornea to the rhabdomeres of the eight retinula cells. 3. In the light-adapted eye, the four cone cells form a crystalline tract, 5 μm in diameter and 40 (μm long, which passes between heavily pigmented primary pigment cells to the rhabdomeres (Figs. 1, 2). 4. In the dark-adapted eye, however, the rhabdomeres are 40 μm closer to the cornea and indent into the cone cells (Figs. 1, 5). There is no crystalline tract. The primary pigment cells are laterally displaced and the diameter of the light path is about 20 μm. 5. Microtubules are abundant in the cone cells and primary pigment cells (Figs. 6, 8). They are oriented in the direction of the cell movement that occurs on light/dark adaptation. 6. These cell movements may act as a pupil, reducing the amount of light reaching the rhabdom in the light-adapted eye.