, Volume 148, Issue 2, pp 143-158

Ultrastructure of the photoreceptor of the planarian Dugesia dorotocephala

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The photoreceptors of the planarian Dugesia dorotocephala were studied by light microscopy and electron microscopy. The eye was found to be rhabdomeric; it is composed of approximately 25 visual cells and a monolayered cup of pigment cells enclosing the light sensitive rhabdome. The pigment cell gave the appearance of having a phagocytic function in addition to regulating the light entering the rhabdome. Extensions of these pigment cells were shown to be the “membranous structure” seen by light microscopy in the open area of the eye. The bipolar visual cell consisted of a perikaryon, axon and a dendritic extension comprised of a stalk, conical body and microvillous rhabdomere. Efferent nerve fibers formed synapses with dendritic spines protruding from receptor stalks. A specialized structure at the transition area between neurotubules and neurofilaments was observed in the conical body. A dense intercellular space occurred between all regions of adjoining visual cells.

This work was supported by National Institute of Mental Health Grant Number 2 R01-MH07603 and General Research Support Grant 5 S01-RR05458-9 given to the Dean of the College of Veterinary Medicine and Biomedical Sciences, Colorado State University.
The authors wish to acknowledge the valuable technical assistance of Les Brown in these studies.