ULTRASTRUCTURE OF A CEPHALOPOD PHOTOPHORE. I. STRUCTURE OF THE PHOTOGENIC TISSUE.

One type of photophore of the deep sea squid Pterygioteuthis microlampas was examined with the electron microscope and its fine structure described. The photogenic tissue is composed of four cell types each with distinctive morphology which suggests their function. The photocytes branch and ramify throughout the central region of the photophore and have an extensive system of microvilli (the photogenic organelle) which are arranged about a central blood filled lumen. The photocytes apparently develop inside a sheath cell and are surrounded by a sheath which is continuous with the basement membrane of the blood vessels. The photocytes and associated sheath cells are surrounded by packing cells whose cytoplasm is replaced with a homogeneous granular material. Finally, cells containing many mitochondria branch and ramify throughout the photogenic area. Apparently the circulatory system is in direct contact with the photocytes, and acellular blood vessels, composed only of basement membrane, are found throughout the photogenic tissue. The similarity between photoproductive organelles and photoreceptive organelles is striking.