2S0 Mr. Macartney’s Observations 
membrane, if it did exist, would have but little effect in 
obscuring the light, and never could serve to extinguish it. 
The regulation of the kind and degree of the luminous 
appearance, does not depend upon any visible mechanism, 
but like the production of the light itself, is accomplished by 
some inscrutable change in the luminous matter, which in 
some animals is a simple operation of organic life, and in 
others is subject to the will. 
It is worthy of remark, that in all the dissections I have made 
of luminous insects, I did not find that the organs of light 
were better, or differently supplied with either nerves or air 
tubes, than the other parts of the body. The power of emitting 
light likewise exists in many creatures which want nerves, 
a circumstance strongly marking a difference between animal 
light, and animal electricity. 
With the exception of the animals above mentioned, the 
exhibition of light depends upon the presence of a fluid 
matter. 
In the pholas dactylus, the luminous fluid is particu- 
larly evident, and in vast quantity ; it is recorded by Pliny, 
that this fluid is like liquid phosphorus, and renders every 
object luminous with which it comes into contact. Reaumur 
also found that it was diffusible in water, or any other fluid 
in which the animal might be immersed.* 
The shining of the scolopendra electrica, I have always 
observed to be accompanied by the appearance of an effusion 
of a luminous fluid, upon the surface of the animal, more 
particularly about the head, which may be received upon the 
hand, or other bodies brought into contact with the insect at the 
* Mem. de 1 ’ Acad, des S.c, 1712. 
