J. A. C. NICOL 307 



in the head. In Lampanyctus, and other teleosts, all the photophores 

 of the head are innervated by the facialis, and those of the trunk are 

 innervated by rami of spinal nerves. 



The sympathetic system is the only longitudinal efferent pathway, 

 traversing the entire length of the fish, that is available after transec- 

 tion of the cord. By assuming that photophore innervation in Porich- 

 thys is similar to that worked out for other teleosts, we can form a 

 picture of the photophores of the head receiving their sympathetic 

 fibers via the facialis, and those of the trunk receiving sympathetic 

 fibers which traverse recurrent gray rami and spinal nerves in each 

 segment. The fact that the photophores are excited by adrenaline is 

 compatible with sympathetic innervation, since this is a normal 

 chemical transmitter of sympathetic fibers, and the photophore nerves 

 may well be, nay probably are, adrenergic in character. Since supra- 

 renal tissue is well represented in teleosts, the possibility remains 

 that the secretion of adrenaline into the bloodstream is a contributory 

 factor in a prolonged response. 



Regulation of Light Emission by Screening Devices 



Screening devices for regulating light emission make use of mus- 

 cular movement, chromatophore movement, or a combination of both. 

 Two fishes, Pfwtoblepharon and Anomalops possess a bacterial lu- 

 minescent organ under each eye. That of Photoblepharon is provided 

 with a fold of opaque tissue which can be raised over the light organ. 

 The organ of Anomalops, on the other hand, can be rotated on a 

 hinge at its anterodorsal end, so as to turn the light surface inward. 

 Steche (1909) has described a pair of antagonistic muscles which 

 serve these organs, but their innervation is unknown. Similar devices 

 are also known in other teleosts and in cephalopods (Harvey, 1922, 

 1952). 



Another screening device in teleosts involves movement of chroma- 

 tophore pigments. Certain fishes such as Acropoma and Leiognathus 

 possess internal glands containing luminous bacteria. The light from 

 these organs shines through the translucent body wall, and the pres- 

 ence of chromatophores in tissues overlying the photogenic organs 

 suggests that they may be involved in regulating light emission. These 

 organs shine continuously, and the chromatophores, by concentration 



