200 
sparkling of the minute meduse and other 
animals, swimming on the surface of the sea, 
when they are dashed against the sides of a 
ship, struck by an oar, or tossed on the foamy 
crests of the waves; and this even while no 
other light is seen excepting just at the points 
where the water is agitated. In experimenting 
with Meduse, Macariney found that, when 
kept in a glass vessel in a state of perfect rest, 
they gave out no light, but that, on the slightest 
movemeni of the vessel, a brilliant flash was 
emitted, which was brightest when the animals 
swam near the surface. Macculloch remarks, 
“* Very often we have found the water crowded, 
even with the largest meduse, yet scarcely be- 
traying themselves by an occasional twinkle, 
when the dash of an oar or any accidental agi- 
tation was sufficient to involve the whole water 
in a blaze of light.” 
5. Loud noises——When any loud noise is 
made near a luminous insect while shining, it 
frequently ceases to give out its light. 
6. Internal movements of the animals them- 
selves,—will, §c.—With regard to insects, we 
have many concurreut testimonies to the fact 
that more light is emitted during the season of 
procreation by most of the species than at other 
times. Sostrikingly is this the case in the Lam- 
pyrides, that the light given out by the female 
has been generally regarded, (although without 
sufficient reasons,) as deStined only to attract 
the attention of her mate. After the eggs are 
deposited, the light gradually decreases in in- 
tensity. 
While it is obvious that, for the most part, 
the emission of light is altogether independent 
of any voluntary effort on the part of the animal 
itself, yet it appears probable that, through 
some means or other, the animal has the power 
of varying the intensity of the light at pleasure. 
We cannot, for instance, imagine that sound 
can have any direct effect on the light-giving 
organs themselves, so as to cause them to shine 
less brightly when loud noises are made near 
them. Such effect must be communicated 
through the animal’s sensorium. It is sup- 
posed by some physiologists that variations in 
the intensity of the light given out by insects 
depend on the quantities of air admitted through 
the trachez in respiration, over which quantities 
the animal’s will seems to exercise some con- 
trol. In observing the luminousness of the 
elater, Spix concluded that this control is so 
perfect, as to admit of the light being wholly 
extinguished by the animal’s preventing the ad- 
mission of air ; and this view is adopted also 
by Treviranus. These changes, however, are 
explained by others, (as by Miiller and Mur- 
ray,) by supposing that, when the light seems 
to fade, the organs are merely withdrawn be- 
hind opaque parts, or, as it were, veiled by a 
curtain. 
In general the light is increased when the 
animal is in motion; and in insects, parti- 
cularly during flight. Macartney observed of 
the beroé, that when it swam slowly near the 
surface of the water, its whole body became 
occasionally illuminated in a slight degree; but 
that, during its contractions, a stronger light 
jssued from the ribs, and that when a sudden 
ANIMAL LUMINOUSNESS. 
shock was communicated to the water in 
it was swimming, a vivid flash was given out. 
That the luminous function is in many an 
mals directly under the control of their 
seems to be proved by the fact, that whil 
under any sudden irritation calculated to alar 
them, they, at first, emit light strongly, yet ¢ 
the frequent repetition or continuance of 
same kind of irritation, they extinguish the 
light, and cannot be excited to shew it agai 
for a considerable time. ‘| 
Il. Artificial circumstances in which light’ 
emitted by living animals, or by which 
emission of it is affected. 
Light-giving animals being removed fix 
their natural situations, and subjected to art 
ficial processes and agents, are found to have 
their lamannennie affected by being exposes 
to, 1. the effects of accumulated elect 
and electrical currents; 2. immersion 
rious fluid and gaseous media; 3. pressure 
their bodies; 4. removal of their lami 
organs, and mutilation of these and of o 
organs ; 5. exposure to various degrees of hi 
and moisture; 6. immersion in vacuo; 7. ¥ 
moval from all foreign sources of light. ¢ 
1. The effects of accumulated electricity @ 
electrical currents. In experimenting on m 
rine luminous animals, Macartney pa 
shock through water in which they were 
ming ; immediately their light was exting 
for an instant, but afterwards became bri 
than before. In reporting the result of a § 
milar experiment, Humboldt merely says th 
the luminousness of the animals was increaset 
after the shock. Macaire subjected glow 
worms to the action of galvanism, and foun 
that when one wire was forced 
body of the insect as far as the luminot 
organs, while the other was applied to the sui 
face slightly moistened, the light became bi 
liant. One galvanic pole produced no effec 
but when insects not shining at the time wer 
placed ina galvanic circle they always beg 
to give out light. This result was not ol 
tained in vacuo, but whenever the air 
admitted, the light reappeared. No effect 
ever seemed to be produced by common 
tricity, howsoever applied. 
2. Immersion in various fluid and gasea 
media.— Luminous marine animals, when 
moved from their native element, and plu 
into fresh water, give out their light fora 
more vividly and more steadily, but afte 
it gradually fades and becomes extinct. Miner 
and vegetable acids, alcohol, and sol 
tions of corrosive sublimate, and the salts, 
produce nearly the same effect; only 
these the light-giving property is more spees 
destroyed. Observers differ in their accom 
of the effects produced by immersion in 
rious gases. Most of those who have eri 
mented in this way have seen the ben of the 
low-worm very rapidly extinguis in hy- 
angen gas ; zr fe s sulphuretted and car 
buretted hydrogen, carbonic acid, chlorine 
nitrogen gases; but Sir H. Davy found tha 
hydrogen gas produced little or no change in 
the state of the light; the same was the result 
of Murray's experiments, who also found 
