. The biology of marine animals. Marine animals; Physiology, Comparative. LUMINESCENCE 549 Polynoid worms such as Polynoe and Acholoe show transitory flashes of light in their elytra when stimulated. The light arises in a single layer of photogenic cells lying on the lower surface of the scale and passes through the latter before reaching the exterior. The photogenic cells are provided with a rich innervation which originates in a central elytral ganglion (Fig. ) (5, 45). Intracellular luminescence is widespread among euphausiids and shrimps, and in some species the photophores are highly
. The biology of marine animals. Marine animals; Physiology, Comparative. LUMINESCENCE 549 Polynoid worms such as Polynoe and Acholoe show transitory flashes of light in their elytra when stimulated. The light arises in a single layer of photogenic cells lying on the lower surface of the scale and passes through the latter before reaching the exterior. The photogenic cells are provided with a rich innervation which originates in a central elytral ganglion (Fig. ) (5, 45). Intracellular luminescence is widespread among euphausiids and shrimps, and in some species the photophores are highly differentiated organs, pos- sessing reflecting layer, screen and lens, associated with a group of photo- genic cells. Among the euphausiids there are three to ten photophores arranged on the eye-stalks, thorax and abdomen. In their simpler form they Elytral nerve Epidermal cell. Fig. Section through Elytrum of Acholoe astericola, Showing Photocytes and Nerve Supply are cup-shaped and the photogenic cells are continued distally into a rod- shaped mass. Bounding the cup externally is a refractive lamellar body. A stout nerve penetrates each photophore, and subdivides and ramifies among the photogenic cells. More complex photophores, such as those of Meganyctiphanes norvegica, contain lenses and a thickened corneal layer in addition (Fig. ). Trojan, who has studied the optical properties of the photophores in Nyctiphanes couchi, has shown that the light-rays are brought into focus in front of the light-organ by a refractor and biconvex lens. The photophores of pelagic shrimps (Caridea and Penaeidea) are distri- buted over the appendages and the thoracic and abdominal sterna in such a way that the light they emit is directed downwards. Their organization is rather simple in Systellaspis (=Acanthephyra) debilis, in which some of the photophores are narrow elongated structures having a cylindrical lens formed by a thickening of the cuticle, and an underlying layer of pho
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