FIJ^WY LIGHT-BEARERS {SURFACE FORMS). 103 



CHAPTER XIII. 



FINNY LIGHT-BEARERS — (SURFACE FORMS). 



ON calm nights the splash of the oars and the fall of 

 spray from the bow of the boat startle many fishes 

 resting at or near the surface, which dart away like comets, 

 leaving a blaze of light behind, and giving the impression 

 that they are light-givers or phosphorescent. This does not 

 always follow ; as, while many possessors of luminous spots 

 undoubtedly approach the surface at night, as Seopelus (Plate 

 X., Fig. 1), many owe their brilliant appearance to the 

 luminosity of the medium in which they swim ; in other 

 words, the vigorous motion of their fins produces the same 

 effect and result that is attained by darting the hand through 

 water bearing phosphorescent animals. If such a display is 

 produced by one fish, we may well imagine that a school 

 moving rapidly would create a light of considerable intensity. 



Drifting over a school of menhaden, and peering down 

 among them, each fish seems outlined in a golden halo ; while 

 coruscations of light appear to flash from the fishes as they 

 move along, the presence of the school being indicated upon 

 the water by a pale luminous spot. 



In more active fishes, as the mackerel, the display is still 

 more brilliant, often presenting a blaze of light upon the 

 surface, visible from the mast-head of a vessel for a long dis- 



