328 
LUMINOSITY OF MARINE ANIMALS. 
light is chiefly emitted by innumerable minute animals, which 
abound in the waters of the surface; whilst the stars and 
ribands are due to larger animals, whose forms are thus bril¬ 
liantly displayed. This interesting phenomenon, when it occurs 
on our own coasts, is chiefly produced by incalculable multi¬ 
tudes of a small creature, termed the Noctiluca y having a nearly 
globular form, and a size about equal to that of the head of 
a minute pin. When these cover the water, and a boat is 
rowed among them, every stroke of the oars produces a flash 
of light; and the ripple of the water upon the shore is marked 
by a brilliant line. If a person walk over sands that the tide 
has left, his footsteps will seem as if they had been impressed 
by some glowing body. And if a small quantity of the water 
be taken up and rubbed between the hands, they will remain 
luminous for some time. The transparency of the little ani¬ 
mals to which these beautiful appearances are due, might cause 
them to be overlooked if they are not attentively sought; they 
somewhat resemble grains of boiled sago in their aspect, but 
are much softer. In the general simplicity of their structure, 
the Noctilucce appear to correspond rather with the Rhkopoda 
(§ 130) than with any other group; but they are distinguished 
by some remarkable peculiarities. 
395. Of the larger luminous forms which are seen to float 
in the ocean-waters, a great proportion belong to the class 
Acalephce. The light emitted by these appears to be due to 
the peculiar chemical nature of the mucus secreted from their 
bodies ; for this, when removed from them, retains its pro¬ 
perties for some time, and may communicate them to water 
or milk, rendering those fluids luminous for some hours, parti¬ 
cularly when they are warmed and agitated. It is probably from 
this source, that the diffused luminosity of the sea is partly 
derived. The secretion appears to be increased in amount, by 
anything that irritates or alarms the animals; and it is from 
this cause that the dashing of the waves against each other, 
the side of a ship, or the shore,—or the tread of the foot 
upon the sand,—or the compression of the animals between 
the fingers,—occasions a greater emission of light. But some 
of these causes may act, by bringing a fresh quantity of the 
phosphorescent secretion into contact with air, which seems 
necessary to maintain the kind of slow combustion on which 
the light depends. 
