upon 'Luminous Animals . 289 
(admitting it to be matter) far exceeds that which could be 
possibly supplied by the sources, from whence it is usually 
supposed to be derived. Tims the luminous appearance of 
some medusae may be continued with the intermission of short 
intervals for an indefinite time, notwithstanding the creature 
be kept in darkness, and without any other food than what a 
small quantity of filtered sea water would afford* The unin- 
terrupted and long continued light that is sometimes evolved 
by the luminous sacs, and the ova of the glow-worm, is 
also inconsistent with the notion of an accumulation and 
subsequent dispersion of a material substance. 
I shall terminate this paper by an enumeration of the 
several conclusions, that are the result of the observations I 
have been able to make upon the phenomena of animal light. 
1 he property of emitting light is confined to animals of the 
simplest organization, the greater number of which are inha- 
bitants of the sea. — The luminous property is not constant* 
but in general, exists only at certain periods, and in particular 
states of the animal's body.— The power of shewing fight, 
resides in a peculiar substance or fluid, which is sometimes 
situated in a particular, organ, and at others diffused throughout 
the animal's body. — The light is differently regulated, when, 
the luminous matter exists in the living bod]/, and when it is 
abstracted from it. In the first case, it is intermitting, or alter- 
nated with periods of darkness ; is commonly produced or 
increased by a muscular effort; and is sometimes absolutely 
dependant upon the will of the animal. In the second case, 
the luminous appearance is usually permanent until it becomes 
extinct, after which it may be restored directly by friction, 
concussion, and the application of warmth ; which last causes. 
