upon Luminous Animals, 275 
The mollusca and worms contain each but a single lumi- 
nous species ; the pholas dactylus in the one, and the nereis 
noctiluca in the other. 
Some species yield light, in the eight following genera of 
insects ; elater, lampyris , fulgora, pausus , scolopendra , cancer , 
lynceus,* and limulus. The luminous species of the genera 
lampyris, and fulgora, are more numerous than is generally 
supposed, if we may judge from the appearance of luminous 
organs, to be seen in dried specimens. 
Amongst zoophytes we find that the genera medusa, beroe,^ 
and pennatula, contain species which afford light. 
The only animals which appear to possess a distinct organ- 
ization for the production of light, are the luminous species of 
lampyris, elater, fulgora, and pausus. 
The light of -the lampyrides is known to proceed from 
some of the last rings of the abdomen, which when not illu- 
minated, are of a pale yellow colour. Upon the internal 
surface of these rings, there is spread a layer of a peculiar 
soft yellow substance, which has been compared to paste, but 
by examination with a lens, I found it to be organized like 
the common interstitial substance of the insect's body, except 
that it is of a closer texture, and a paler yellow colour. This 
substance does not entirely cover the inner surface of the 
rings, being more or less deficient along their edges, where 
it presents an irregular waving outline. I have observed in 
the glow worm, that it is absorbed, and its place supplied by 
*'The animal discovered by Riville off the coast of Malabar in 1754, is certainly 
a testaceous insect, and appears to belong to the genus lynceus of Muller. 
f The luminous zoophyte for which Peron has lately instituted the new genus 
pyrosoma, appears to me to be a beroe, and only worthy of a specific distinction. 
