LUMINOUS SHAKK. 429 



not perceptibly increased by agitation or friction. When the 

 shark expired, (which was not until it had been out of the water 

 more than three hours,) the luminous appearance faded entirely 

 from the abdomen, and more gradually from other parts ; linger- 

 ing longest around the jaws and on the fins. 



The only part of the under surface of the animal which was 

 free from luminosity was the black collar round the throat ; and 

 while the inferior surface of the pectoral, anal, and caudal fins 

 shone with splendour, their superior surface (including the upper 

 lobe of the tail fin) was in darkness, as were also the dorsal fins, 

 and the back and summit of the head. 



Mr. Bennett is inclined to believe that the luminous power of 

 this shark resides in a peculiar secretion from the skin. It was 

 his first impression that the fish had accidentally contracted some 

 phosphorescent matter from the sea, or from the net in which it 

 was captured ; but the most rigid inyestigation did not confirm 

 this suspicion, while the uniformity with which the luminous 

 gleam occupied certain portions of the body and fins, its per- 

 manence during life, and decline and cessation upon the approach 

 and occurrence of death, did not leave a doubt in his mind but 

 that it was a vital principle essential to the economy of the 

 animal. The small size of the fins would appear to denote that 

 this fish is not active in swimming ; and, since it is highly pre- 

 daceous and evidently of nocturnal habits, we may perhaps 

 indulge in the hypothesis, that the phosphorescent power it 

 possesses is of use to attract its prey, upon the same principle as 

 the Polynesian islanders and others employ torches in night- 

 fishing. 



Some of the lower sea-plants also appear to be luminous. 

 Thus, over a space of more than 600 miles (between lat. 

 8° N. and 2° S.), Meyen saw the ocean covered with phospho- 

 rescent Oscillatoria, grouped together into small balls or glo- 

 bules, from the size of a poppy-seed to that of a lentil. 



But if the luminosity of the ocean generally proceeds from 

 living creatures, it sometimes also arises from putrefying organic 

 fibres and membranes, resulting from the decomposition of those 

 living light-bearers. "Sometimes," says Humboldt, "even a 

 high magnifying power is unable to discover any animals in the 

 phosphorescent water, and yet light gleams forth wherever a 

 wave strikes against a hard body and dissolves in foam. The 



