ELECTRON MICROSCOPE STUDY OF THE DISTAL PORTION OF A PLANARIAN RETINULAR CELL

¹ Department of Zoology, University of Wisconsin—Milwaukee, Milwaukee 3, Wisconsin

1. Anterior portions of Dugesia tigrina were prepared for electron microscopic examination by fixing in osmium tetroxide buffered at pH 7.2, embedding in methacrylate polymer, and sectioning at 0.025 µ

2. The rhabdome of the retinula is composed of longitudinally oriented lamellae whose distal portions are differentiated into bulb-like swellings bearing smaller lamellae. The "middle region" of the retinula contains lamellae that appear, in some instances, to extend into the rhabdome.

3. Little analogy can be drawn between the fine structure of the retinula of the planarian eye and that of the rods and cones of the vertebrate eye.