THE FISH OF THE DEEP SEA 161 



extremity of the cranial cavity.' They are covered 

 by the upper walls of the skull, which is extremely 

 thin and completely transparent in the region lying 

 over them. ' They are membranous structures 

 0'4 mm. in thickness marked by hexagonal areas 

 about 0'04 mm. in diameter. When their surface is 

 viewed by reflected light the appearance is that of a 

 number of glistening white isolated short columns 

 standing up in relief from its basal membrane.' Each 

 hexagonal column is composed of a number of trans- 

 parent rods disposed side by side at right angles to 

 the outer surface of the organ, with their bases applied 

 against the concave surface of a large hexagonal 

 pigment cell, one of which forms the basis of each 

 hexagonal column. It is still very doubtful what 

 are the true homologies of this extraordinary phos- 

 phorescent organ, but Moseley was of opinion that, ; on 

 the whole, it seems not unlikely that the remarkable 

 head organs of Ipnops may be regarded as highly 

 specialised and enormously enlarged representatives 

 of the phosphorescent organs on the heads of such 

 allied Scopelidae as Scopelus rafinesquii and Scopelus 

 metopoclampus. It may be conceived that in Ipnops 

 the supra-nasal and sub-ocular phosphorescent organs 

 of these species on either side have united and 



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