Derivatives of Cilia in the Distal Sense Cells of the Retina of Pecten

The scallop, Pecten, a bivalved mollusk, has approximately 100 brilliantly colored blue-green eyes a millimeter or so in diameter located along the free margins of the mantle. Eaz.h eye contains a double retina which is separated from the lens by a thin connective tissue septum. Just beneath the septum lies the distal retina with its two cell types: the distal sense cell (Dakin's (1910) terminology), which is associated with the distal ramus of the optic nerve, and the external interstitial supporting cell. The proximal retina (which will be described in a subsequent communication) is just beneath the distal retina, and it contains rod cells associated with the proximal ramus of the optic nerve and internal interstitial supporting cells. This note describes observations concerning the fine structure of appendages on the specially differentiated septal border of the distal sense cells.