The distribution of luminescence in Ophiopsila californica and Amphipholis squamata is described on the basis of image intensification, fluorescence microscopy, and histological techniques. 2. Luminescence appears to be intracellular. 3. The photogenic cells, termed photocytes, can be identified in histological sections by observation of 460 nm excited fluorescence and appear to have two components: varicosities and processes. The processes are morphologically similar to the neurons of the peripheral nervous system and the radial nerve cord. 4. The theory of gland cells as sites of luminescence in Ophiopsila spp. and Amphipholis squamata is not supported. 5. The emission spectra of luminescence in O. californica and A. squamata are broad with a half band width of 71 nm and an approximate emission maximum at 510 nm. 6. Fluorescence appears only after the onset of luminescence.
