THE GLOW WO Elk* S LIGHT-EMITTING APPARATUS. 321 
insect over its light- organs. This may perhaps be true of the 
living insect, but does not account for the intermittent function 
persisting in the excised organ , nor for the effect of stimuli and 
narcotics applied to the organ itself. The same observer 
speaks of the capsule of the organ as being superficially 
mapped out by division into separate facts, the use of which 
he compares with refracting lenses in multiplying and inten- 
sifying the light from within. This conformation of the 
capsule has not been described by other writers, nor has the 
present writer been able to confirm it. 
The obvious purpose of the tracheal distribution is admis- 
sion of oxygen into the parenchyma, and the oxidation of the 
cell contents. It becomes important, therefore, to determine 
the chemical composition of the organic matter of the cells : 
whether it be, as Macartney, Carus, Phipson, and others 
believe, some form of hydrocarbon (i. e., fat ) ; or, as Macaire 
(Bibliothegue TJniverselle) , Kolliker, and others believe to 
have demonstrated, albuminous. The first assumption would 
support the theory of combustion, the second that of meta- 
morphosis and evolution of force (or light as a correlation 
of force). 
To the objection that may be raised against the animal 
character of the function, namely, that the persistence of the 
luminous appearance in the organic substance for so long a 
time after its removal from the insect's body indicates a purely 
physical or chemical cause of the act, it may be replied that 
the proofs of functional activity of animal tissues removed 
from the body are innumerable. Until the vitality of a tissue 
is exhausted , its proper function continues, after which general 
decomposition first ensues. Setting aside the unquestioned 
activity of the simple tissues of the lower animals under cir- 
cumstances which demonstrate their possession of a vis 
propria separate from the collective vitality of the animal, 
we have sufficient and decisive evidence that nerve and muscle 
function, and even so compound an act as the secreting 
function of a gland, may persist so long as vitality exists in 
the parts. There is, therefore, no ground to deny the con- 
tinuance of a light-producing function under similar con- 
ditions, than there is to deny muscular irritability or nerve 
excitation. 
Now the theory of “ combustion " and that of “ metamor- 
phosis " are both based on oxidation," which is, in a 
certain sense, a physical act ; but, occurring in animal tissues, 
cannot be separated from the vital acts by which it is regu- 
lated. The evolution of sensible heat may or may not be an 
accompaniment of the vital process, and the term “ combus- 
tion," as applied to it, appears objectionable, as leaning too 
