LUMINOUS SHARK. 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 investigation 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° §.), 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 
