LETTER XXV. 
ON LUMINOUS INSECTS. 
We boast of our candles, our wax-lights, and our 
Argand lamps, and pity our fellow-men who, ignorant 
‘of our methods of producing artificial light, are con- 
demned to pass their nights in darkness. We regard 
these inventions as the results of a great exertion of 
human intellect, and never conceive it possible that 
other animals are able to avail themselves of modes of il- 
lumination equally efficient; and are furnished with the 
means of guiding their nocturnal evolutions by actual 
lights, similar in their effect to those which we make 
use of. Yet many insects are thus provided. Some 
are forced to content themselves with a single candle, 
not more vivid than the rush-light which glimmers in 
the peasant’s cottage; others exhibit two or four, which 
cast a stronger radiance; and a few can display a lamp 
little inferior in brilliancy to some of ours. Not that 
these insects are actually possessed of candles and lamps. 
You are aware that I am speaking figuratively. But 
Providence has supplied them with an effectual substi- 
tute—a luminous preparation or secretion, which has 
all the advantages of our lamps and candles without their 
inconveniences; which gives light sufficient to direct 
