ELECTRON MICROSCOPY ON THE PHOTORECEPTORS OF AN ANTHOMEDUSA AND A SCYPHOMEDUSA

Abstract

Some hydrozoan and scyphozoan medusae are known to have photoreceptors called eye spots or ocelli. In the hydromedusae the ocellus is situated at the aboral base of each tentacle, while the eye spots in the scyphomedusae are located on the marginal bodies called rhopalium near the bell margin. Studies on the structure of the ocelli of the hydromedusae have been limited to Polyorchis penicillatus. Though earlier investigators have reported a lens or Glaskorper by the light microscopy (7, 8). EAKIN and WESTFALL (4, 5) have disproved it and have further shown electron-microscopically that the photosensory cells belong to the primitive photoreceptor of the ciliary type (2). As regards the structure of scyphomedusan eyes, on the other hand, the classical observation on Aurelia aurita of SCHEWIAKOFF (1889), cited by BuLLOCK (1) is probably the only one which has been done so far. Work has been done in our laboratory on the physiological and photochemical aspects of the ocelli in the anthomedusa, Spirocodon saltatrix (11, 12, 13 and 14). However, since the basic morphological information which is important for interpreting experimental results is so scanty as above, we started to study the fine structure of cnidarian photoreceptors for the purpose of elucidating organization of sensory cells as well as their interrelationships with the second order neurons.