LUMINESCENCE 541 



LUMINESCENT GLANDS AND ORGANS 



The production of light is due to a chemiluminescent reaction in which a 

 suitable substrate is oxidized and the accompanying energy transforma- 

 tions appear as visible light. The luminescent material is usually fabricated 

 by the animal itself, but there are some instances in which the animal 

 normally harbours luminescent bacteria responsible for the light emitted. 

 True animal luminescence may be entirely an intracellular process, or it 

 may arise in photogenic material which is secreted by the animal and dis- 

 charged to the exterior to appear as extracellular luminescence. There are 

 also some forms that possess more than one kind of light-organ and that 

 luminesce in different ways. For example, the pelagic shrimp Systellaspis 

 debilis has typical photophores as well as luminescent glands that release 

 an extracellular secretion. 



Extracellular Luminescence 



In animals showing extracellular luminescence the light-producing glands 

 are unicellular or multicellular structures which are usually restricted to 

 definite circumscribed regions of the body. These gland cells are sometimes 

 of two types, producing recognizably different secretory granules, both of 

 which are concerned in the production of light. 



In the nemertine Emplectonema kandai the photogenic cells that produce 

 the luminescent secretion are distributed over the whole surface of the 

 animal. The tubicolous polychaete Chaetopterus variopedatus is a well- 

 known luminescent form which gives off a luminous secretion from certain 

 glandular areas (Fig. 13.2). These are the peristomial tentacles, the aliform 

 notopodia, the dorsal tubercle and fans, and all notopodia of the posterior 

 region of the body. The glandular cells responsible for the secretion con- 

 tain closely packed eosinophilic granules, and are scattered singly in the 

 epidermis or massed into distinct glands (Fig. 13.3). These glands are 

 particularly well developed on the aliform notopodia, where they give rise 

 to a luminous material which is suspended in mucus and dispersed by 

 ciliary action in the surrounding sea water. In other regions of the body, 

 however, the luminescence is more transitory and the secretion adheres to 

 the body surface (6, 36, 42). 



In cirratulid and terebellid worms a luminescent "slime" is secreted by 

 the body and tentacles. The tentacles of Poly cirrus bear patches of lumi- 

 nescent cells, loaded with eosinophilic granules, which are discharged to 

 the exterior. In Odontosyllis the production of light occurs during spawn- 

 ing. A luminous secretion is discharged into the water and this appears to 

 arise in photogenic glands lying at the base of the parapodia and provided 

 with ducts to the exterior (7, 8). 



Among Crustacea luminescence in the ostracod Cypridina has been more 

 extensively studied than in any other form. The secretory cells in this 

 animal are localized in a luminous gland which lies on the upper lip near 

 the mouth. The gland cells are arranged in groups and discharge by pores 



