REPORT ON THE DEEP-SEA FISHES. 301 



as they are large and striking in ai^pearance, they strongly (;haracterise the species which 

 possess them. 



In the diflFerent species they are distributed as follows :— 



Argyropelecus hemigymmis. — A row of six anterior to the pectoral fin, a row of 

 twelve ventral, close to the median plane of the body, and three groups on the sides, 

 ill the vicinity of the anal fin. The groups are formed by the breaking up of the two 

 lateral rows of phosphorescent organs observed in other fishes, the upper row furnishing 

 three, and the lower two groups. All the organs point downwards. 



Sternoptyx diaphana. — A row of nine large organs on the ventral side, close to the 

 median plane, representing the lower row, and two groups of three organs in each, above, 

 on the side, representing the upper row (PI. LXX. figs. 15, 17). All point downwards. 



Scopelus henoiti. — One organ in the middle of the back, behind the dorsal fin, 

 pointing backwards. The organs of the lateral rows have retained their original shape 

 and distribution. 



Scopelus, otlier species. — I cannot give an account of the distribution of these organs 

 in other species, as Leydig does not specially mention these peculiar unpaired organs 

 behind the dorsal fin which are so characteristic of Scopelus. Sometimes there are more 

 organs than one in that locality, in some species as many as five, one behind the 

 other, and they always point backwards. 



Gonostoma denudatum. — In two lateral rows like the composite organs without 

 reflectors (Leydig). 



h. Structure. 



a. General. 



The structure of these organs is more comjjlicated than that of the organs without 

 reflectors, and there are very essential differences between the two, although they are 

 similar to a certain extent in shape, and formed on the same principle. They may be 

 single and isolated, as for instance the organs on the back of Scopelus henoiti, here 

 designated "stern-chasers"; the rule, however, is that several are placed together, with 

 their sides in contact, and that theii- spherical interior portions coalesce to a certain extent. 

 Buch a coalescence of course produces a canal, from the outer side of which the cup-shaped 

 portions of the organs project (PI. LXX. figs. 17, 18, 20). Such structures are never 

 produced by the union of phosphorescent composite organs without reflectors. These 

 organs with reflectors are always very oblique, so much so that the axis is inclined 

 towards the surface of the fish at an angle, never exceeding 10°. Generally this angle 

 is smaller and the axis often appears nearly parallel to the surface. The spherical 

 portion is more elliptical than in the organs above described, and appears sac-shaped. 



