ANIMAL LUMINOUSNESS. 
the glow-worm continue to shine in carbonic 
acid gas. Immersion in oils of all kinds de- 
stroys the light-giving property in most of the 
Insects endowed with it; but in Lampyris 
italica, Carradori found that the light conti- 
nued to be emitted when the luminous part 
of the body was plunged into oil. 
3. Pressure of their bodies—It has been 
observed that shortly after the death of the in- 
Sect, the light-giving organs of elater emit light 
freely when the body is bruised, and in general 
mechanical irritations of all kinds cause a cer- 
tain degree of increase in the intensity of the 
light given out. Some animals, as pennatula, 
seem to emit their light rarely, excepting in 
such circumstances. 
4. Removal of the luminous organs, and mu- 
tilation of these and of other organs.—The 
luminous organs may be cut out from the 
bodies of glow-worms and fire-flies without the 
peculiar property of the organs being imme- 
diately destroyed. The emission of light can 
for some time be re-excited by slight me- 
chanical irritations ; as by touching the organs 
with the point of a pin. Those of the glow- 
worm have been seen to shine for two or three 
days after excision, when slightly moistened. 
with water, heated or electrified. In experi- 
menting on the same insect, Todd found that 
the light was extinguished within six minutes 
after the head was cut off; as also when the 
luminous rings were cut into, but was renew- 
able by the application of heat. Sheppard 
removed the luminous matter from a glow- 
worm; the wounds healed within two days, 
and the body became again filled with new 
light-giving substance.* 
5. Exposure to various degrees of heat and 
moisture.—Light-giving insects in general do 
not shine at any temperature below that of 
53° Fahr. Macaire took some glow-worms 
that had been kept for some time at a tem- 
perature of 50° Fahr., plunged them into water 
at 55°, and gradually raised the temperature. 
Light was emitted for the first time at 77°, 
and increased in intensity until the water was 
at 105°. At this temperature the animals died, 
but the light continued until the temperature 
had reached 134° 5, when it wholly disap- 
red. When glow-worms are thrown alive 
into water heated to 110° and upwards, they 
die instantly, but at the moment emit a brilliant 
light. When they are exposed to an artificial 
cold suddenly, they perish at any degree below 
the freezing point of water; but the light ma 
be partially restored by a temperature of 70°, 
although the animals shew no other sign of 
vitality. When the insects are dried artificially, 
the light is extinguished, but it may be restored 
by their being again moistened. 
6. Immersion in vacuo.—W hen glow-worms 
are placed in vacuo, their light fades, but re- 
appears on admission of air. ; 
7. Removal from all foreign sources of light. 
—lIf luminous insects be confined in a dark 
place, they shine little in the early part of the 
day, but long before night they begin to do so; 
* Kirby and Spence’s Entomology, ii. 426. 
201 
although generally, in their native situations, 
they do not emit light until the twilight. If 
the confinement in a dark place be protracted, 
they do not shine so brightly as after having 
seen the sun during the day. 
1V. Seat of luminousness in different animals. 
—In most of the luminous animals that infobit 
the ocean, a great part of their surface seems 
to be endowed with the property of forming, 
and pouring out, a mucous fluid, which contains 
the luminous matter, and is frequently mis- 
cible with water and other fluids. This some- 
times so entirely covers the whole animal as 
to cause it to emit light from every point of its 
surface; but more generally when the animal 
is swimming, the light is seen to proceed only 
from certain regions. Some of the meduse, 
even of the largest size, emit light from a very 
small point, particularly when the luminous 
organ is placed in the central parts of the body. 
When the light is vivid, it seems to be larger 
than it really is, from the refracting power of 
the gelatinous tissues through which it passes. 
Occasionally the luminous point has not a 
diameter equal to the 1-200th of that of the 
animal itself. In cydippe pileus and oceania 
pileata of the Baltic, Ehrenberg finds that the 
light issues solely from the vicinity of the 
ovaries, and in oceania hemispherica, from the 
bases of the cirri. Pholas dactylus gives out 
light most strongly from the internal surface 
of its respiratory tubes. The luminous mucus 
is sometimes poured out even by very small 
animals in such quantity as to leave a lumi- 
nous wake behind them, as in an instance 
mentioned by Quoy and Gaimard. These ob- 
servers saw such luminous lines formed in the 
paths of certain extremely small creatures, so 
transparent that their forms could not be dis- 
tinctly made out. The positions of their bodies 
were marked in the water by bright spots, 
which were followed in their course by lumi- 
nous wakes, at first about an inch in breadth, 
but afterwards by the movements of the water 
spread out to the breadth of two or three 
inches. This luminous mucus is supposed to 
be the seat also of the remarkable stinging 
roperty possessed by many of the acalephe. 
t retains its luminousness in some instances 
for a day or two after being emitted by the 
animal, but loses it whenever putrefaction 
commences. 
But although this luminous mucus be so ge- 
nerally secreted and emitted by marine ani- 
mals, it is evident that the light given out by 
many of them has its seat in certain organs 
more or less internal, whence it proceeds in 
gleams and momentary flashes that seem to 
depend only on the movements of some im- 
ponderable agent. The exact position and re- 
lations of these organs can seldom be satis- 
factorily discovered, but in some crabs and mi- 
nute crustaceous animals that emit light, it is 
observed to proceed from the central organs of 
the nervous system. In other crustacea the 
whole body seems to be full of light, which is 
emitted, as at so many windows, through the 
translucent membranes interposed between the 
segments of the crust. Dr. Macculloch con- 
