FACTS AND THOUGHTS ABOUT LIGHT-EMITTING ANIMALS. 241 
similarity of the glow of the Lampyris , and the light accom- 
panying the oxidation of phosphorus, and there is not enough 
(if there be any) of the element in these tiny things to account 
for the special phenomena. 
Fungi, decaying fish, and the flesh of lobsters are luminous 
under certain conditions, but the phenomena differ from those 
of the living animal, and are no more to be satisfactorily com- 
pared, than they are with the sharp emanation of light on the 
crystallization of tartar emetic, or with the results of the mixture 
of hydrochloric acid and arsenic during its crystallization. 
It is evident that in some animals there is no special photo- 
genic structure; that in others it is present as highly refractive 
cell contents ; and in the Insecta there are aggregations of these 
cells into special organs, which are supplied with air-tubes, nerves, 
and blood. It is equally clear that whilst in the first and second 
groups, artificial irritation and the natural stimulus of the move- 
ment of the sea-water increase the light, and even induce it, there 
is still the power of intrinsic self-illumination. Quatrefages points 
out the extreme sharpness and brightness of the localized spots of 
light on Noctiluca , and insists that in a corresponding mass of 
them there is as much light given out as from the organ of 
Lampyris. There is, however, this difference between the light. 
It is extinguished in both in vacuo , but it returns only in the 
Lampyris. Two sets of phenomena are probably present, and in 
the simplest animal the physical cause of the light is probably 
different from that in the beetle. Certain it is, that all the agents 
which produce contraction of the protoplasm of Noctiluca deter- 
mine the light, and if a persistent contraction is set up, the 
light is equally persistent, and death results. As the light 
comes from spots about the region where growth, the deposition 
of fresh protoplasm and its differentiation into minute granules 
are in full operation, and as moderately careful experiment has 
proved that there is no increase of temperature accompanying 
the light, the cause of it cannot be referred to “ combustion,” 
to oxidation, or to phosphorus, but to local and then general 
molecular movement of intense rapidity, which can produce 
light waves. In the instance of the Pholas large quantities of 
this luminous substance can be collected, but the temperature 
bears no relation to the light. If twenty or thirty female 
glowworms are put on the hand, which is rendered as visible as 
by the light of a candle, there is no appreciable temperature 
above that of the cold, clammy insect. The notion of oxidation 
of matter producing brilliant light without a measurable amount 
of heat is of no great value ; and certainly if a female Lampyris 
glowing on damp grass so as to be luminous entirely underneath, 
and to have her light visible for many paces off, could evolve a 
corresponding or relational amount of heat, she would be fried. 
NEW SERIES, VOL. III. — NO. XI. E 
