150 INTERNAL ANATOMY OF INSECTS. 
gingly communicated to me. He remarks that in a box 
in which glow-worms were kept — five luminous specks 
were found secreted by the animal, which seemed to glow 
and were of a different tinge of light. One put into olive 
oil at eleven p. m. continued to yield a steady and unin- 
terrupted light until five o'clock the following morning, 
and then seemed, like the stars, to be only absorbed by 
superior effulgence. The luminous spherical matter of 
the glow-worm is evidently enveloped in a sac or capsule 
perfectly diaphanous, which when ruptured discloses it 
in a liquid form, of the consistency of cream. M. Ma- 
caire, he observes, in the Bibliotheque Universelle, draws 
the following conclusions from experiments made on the 
luminous matter of this animal ; — that a certain degree 
of heat is necessary to their voluntary phosphorescence 
— that it is excited by a degree of heat superior to the 
first, and inevitably destroyed by a higher — that bodies 
which coagulate albumen take away the power — that 
phosphorescence cannot take place but in a gas contain- 
ing no oxygen — that it is not excited by common elec- 
tricity, but is so by the Voltaic pile — and lastly, that 
the matter is chiefly composed of albumen. 
xii. Fat. There is one product found in the body of in- 
sects most copiously in their larva state, but more or less 
also in the imago, which may be called their fat. In the 
former it is a many-lobed mass, occupying the whole ot 
the interior, except the space that is required for the 
muscles and the internal organs, which it wraps round 
and protects. It is contained in floating membranes, 
very numerous, which fill all the interstices, and assume 
the appearance sometimes of small globules, and some- 
times of a thickish mucilage, which easily melts and in- 
