NATURAL HISTORY STUDIES 



act as searchlights, playing over the floor of the sea. 

 Some of them are simple, but others have a compli- 

 cated optical apparatus with some or all of the follow- 

 ing structures pigment layer, reflector, lens, and 

 diaphragm. 



In two surface fishes of the Malay Archipelago 

 (which have very big mouthfuls of names 

 Anomalops katoptron and Photoblepharon palpebralis) 

 there are large luminous organs about the head, 

 which seem to give out a constant light without 

 requiring any particular stimulus. The lumin- 

 escence has its seat in material secreted by glandular 

 cells, and occurs outside the cells in the cavity of 

 the gland. The luminescent organ can be, so to 

 speak, extinguished by a downward movement, 

 which possibly takes place when an enemy appears 

 on the scene. 



A very remarkable deep-water fish, named 

 Lamprotoxus, has been described from the south- 

 west coast of Ireland. It has a filamentous feeler 

 many times longer than the body. The colour 

 of the scaleless skin is velvety-black and the feeler 

 or barbule is grey. A purplish-grey band of 

 luminous cells, partially embedded in the skin, 

 forms a closed loop on the anterior part of the body. 

 There is also a large " lamp " behind and slightly 

 below the eye, shut in by skin save for a narrow 

 slit ; and there are numerous minute lamps. 



There is little direct evidence as to the use of 

 luminescence, and, as we have said, there are pro- 

 bably many cases where it is of no use. But this 

 cannot be the case when it is associated with very 



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