252 Remarks on Marine 



give an occasional spark as it passes by, when the dipping of 

 an oar, or the drawing of a bucket of water, is sufficient to 

 render the whole around luminous. 



It is by such a test as this, therefore, that a naturalist will be 

 guided in his pursuit after these animals. But it is proper to 

 remark that it is often very difficult to take them, even when we 

 are certain that they abound in the water ; and this cause, like 

 others, has often made it to be supposed that the water itself pos- 

 sessed a luminous property, because no animals appeared in a 

 bucket when filled with it. A few bright lights produce a con- 

 siderable effect in the night, so as to make the sea appear much 

 fuller of sparks than it really is ; and it is easy for a body so 

 small as the ship's bucket to miss the animals by which they are 

 produced. Moreover, as many of these creatures, and particu- 

 larly the medusae, swim near to the surface, they are apt to slip 

 out with the wave which is produced by lifting the bucket out of 

 the water ; so that it sometimes requires many attempts before 

 one can be secured. 



There is another circumstance which is also an occasional 

 source of error respecting the existence of these animals in the 

 water when brought up ; even when it is highly luminous along- 

 side the vessel. Whether from fatigue, or from caprice, or from 

 some voluntary efforts for an unknown purpose, they often refuse 

 to show their light, even when violently agitated or injured ; 

 and, in all cases, when they have been compelled to shew it for 

 a few seconds by violence, they again become dark and refuse 

 to shine any longer. It is not unlikely that this is the effect 

 of exhaustion ; because after a repose of some little time, a 

 fresh disturbance often causes them to give light again. A natu- 

 ralist, unaware of this circumstance, may often imagine that he 

 has failed in procuring specimens, even when the bucket is 

 crowded with them. 



Another circumstance leads to deceptions in these cases. In 

 many of the luminous worms and insects, the spot of light ap- 

 pears much larger, if it is not really so, than the body of the 

 animal ; and very often a species which is invisible under ordi- 

 nary circumstances, or only to be seen by bringing it opposite 



