$+ Observations upon Luminous Animals. 
ganization 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 il- 
luminated 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 co- 
lour. This substance does not entirely cover the inner sur- 
face of the rings, being more or Jess 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 a common interstitial substance, after the season 
for giving light is past. 
The seemcnts of the abdomen, behind which this peculiar 
substance is situated, are thin and transparent, in order to 
expose the internal illumination. , 
The number of luminous rings varies in different species 
of lampyris, and as it would seem at different periods in 
the same individual, : 
Besides the luminous. substance, above described, I have 
discovered in the common glow-worm, on the inner side of 
the last abdominal ring, two bodies, which to the naked eye 
appear more minute than the head of the smallest pin, 
They are lodged in two slight depressions, formed in the 
shell of the ring, which is at these points particularly trans- 
arent. .On exainiuiny these bodies under the microscope, 
found that they were sacs contaiping a soft yellow sub- 
stance, of a more close and homogeneous texture thau that 
which lines the inner surface of the rings, The membrane 
forming the’sacs appeared to be of two. layers, each of 
which is composed bya transparent silvery fibre, in the same 
manner as the internal membrane of the respiratory tubes of 
insects, except that im this case the fibre passes in a_ spiral 
instead of a circular direction. This membrane, although 
so delicately constructed, is so elastic as to preserve its form 
after the sac is ruptured and the contents discharged. 
The light that proceeds from these sacs is less under the 
control of the insect than that of the luminous substance 
spread on the rings: it is rarely ever entirely extinguished 
in the season that the glow-worm gives light, even during 
the day; and when all the other rings are dark, these sacs 
often shine brightly. a . 
Th¢ 
