204 
tion of an imponderable agent by the nervous 
systems of the animals, just as the electrical 
fishes give their shock without the interposition 
of any visible or ponderable secretion. In this 
view we may regard the luminous organs as 
laying the same part in relation to the evo- 
ution of light as the electrical organs of the 
torpedo do to the production of the shock. 
The single fact of luminousuess continuing in 
the organs or in their effused fluids, after they 
have been removed from the body of the ani- 
mal, seems to point to a great difference ex- 
isting between the two classes of phenomena 
which we have just compared, in certain ani- 
mals; but it may be that the difference is 
more ap nt than real; for this fact may be 
explained by supposing that a phosphoric sub- 
stance really does enter into the composition 
of the light-giving organs; and yet we may 
with great probability conjecture that it is not 
the chief agent in causing the phenomena of 
luminousness. It remains, then, for future in- 
quirers to determine the chemical composition 
of the luminous organs, and the fluids emitted 
by the animals, the phenomena of whose lu- 
minousness seem to be irreconcileable with the 
idea of their being dependent on the nature 
of these fluids; if they be found to contain 
phosphoric matter, it may be concluded that, 
as this does not appear to be essential in them 
to the production of the phenomena of lu- 
minousness, so neither may it be in other ani- 
mals, in which it is believed to be the chief 
agent in the manifestation of their light-giving 
function. 
To this theory, (which is only a combination 
of the two most generally received in modern 
times,) we do not, in the facts which have 
come under our notice, see any serious objec- 
tion. The only argument adduced against 
Macartney’s theory by Tiedemann and other 
physiologists, who have carefully considered 
the facts of the case, is founded on the circum- 
stance of the light continuing, in a certain 
degree, for some time after the death of the 
animals, which, of course, cannot be supposed 
to be owing to the continued operations of the 
nervous system. This posthumous light, how- 
ever, may depend on the phosphorescence of 
the luminous organs or their effused fluids in 
virtue of their composition, while the full evo- 
lution of light during life may be produced 
chiefly by the play of imponderable agents in 
and from the nervous system, independently, 
in some cases, of the chemistry of the fluids ; 
in other cases, aided and modified by the nature 
of these and by the structure of peculiar organs. 
It is scarcely necessary to take particular 
notice of the various other theories that have 
been suggested, as the facts stated in the pre- 
ceding part of the article are sufficient to set 
them aside. 
VIII. Uses of animal luminousness—We 
know nothing certainly with regard to the 
uses of the light-giving function ; but as almost 
all observers have remarked that male insects 
seem to be attracted towards their mates by the 
brilliancy of the light emitted by the latter, it 
ANIMAL LUMINOUSNESS. 
has been generally supposed that the lumin 
ness is subservient to the generative function 
Although it may be so to a certain extent, it i 
obviously not essentially connected with i 
even in the glow-worm ; for the light endure 
long after the season of love is past. Sor 
have conjectured that the light may sometim 
be the means of preserving its i 
the destructive attacks of enemies. Thus Shy 
pard observed a large beetle running rount 
shining scolopendra, as if wishing to attack 
but seeming to be scared by the light. 
may imagine, also, that the light enab! 
possessors to see surrounding objects at 
and so to thread their way in safety through 1 
darkest places. te 
Considering that, in the ocean, there is ab: 
lute darkness at the depth of 800 or 1000 f 
at least that, at such depths, the li 4 
sun ceases to be transmitted, Maccu , 
suggested* that, in marine animals, theirlum 
nousness may be “a substitute for the light 
the sun,” and may be the means of enab 
them to discover one another, as well as th 
prey. He remarks, “It seems to be partic 
cularly brilliant in those inferior animals whi 
from their astonishing powers of reproducti 
and from a state of feeling apparently Iii 
superior to that of vegetables, appear to 
been in a great measure created for the sup 
and food of the more perfect kinds.” 
IX. Luminousness of animals not innat 
and other allied phenomena.—We have + 
counts of the surface of the human body aj 
pearing luminous in consequence of ph 
phoric matter being largely mixed with t 
sweat in the course of various diseases. T 
urine also both of men and several of t 
lower animals is occasionally luminous und 
similar circumstances. It is said that the urit 
of Viverra mephitis and V. putorius is 
ways so.t 
The eyes of human albinoes, almost all 
mammalia which possess a tapetum lucidu 
as also those of some birds of prey, serpent 
and insects, seem to shine in a feeble ligi 
from the reflexion and concentration of th 
rays falling upon them from external object 
Pallas thought that this light was developed 
the retina, and regarded it as an electrical f 
nomenon. But it has been plainly prove ib 
Prevost, Gruithuisen, and Esser,{ that # 
shining of the eye depends, in most cases, 0 
reflexion of light. They found that there wa 
no appearance of luminousness in absolw 
darkness; and that the eyes of dead anim: 
gave the same effect as those of the livin 
when placed in similar circumstances. 
It would appear, however, from some obser 
vations made by Rengger on the eyes of | 
certain South American ape, ( Nyctipithecus 
trivirgatus, ) that there is reason to believe im 
3 
% 
ps 
* ro 
* Edin. Encycl. art. ‘¢ Phosphorescence.” pe 
+ Langsdorff, Reise. ii. 184. : 
t Edin. New Phil. Jour. ii. 164. i 
§ See also Hessenstein, de Luce ex quorund 
animal. oculis prodeunte, atque de Tapeto lucido, 
Jenz, 1836. 
