328 LUMINOSITY OF MAKINE 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, 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 Noctilucos appear to correspond rather with the Rhizopoda 

 ( 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 tune, 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. 



