4.24 LUMINOUS INSECTS.. 
This light he found to be less under the control of the 
insect than that from the adjoining luminous substance, 
which it has the power of voluntarily extinguishing, not 
by retracting it under a membrane, as Carradori ima- 
gined, but by some inscrutable change dependent upon 
its will: and when the latter substance was extracted 
from living glow-worms it afforded no light, while the 
two sacs in like circumstances shone uninterruptedly for 
several hours. Mr. Macartney conceives, from the radi- 
ated structure of the interstitial substance surrounding 
the oval yellow masses immediately under the trans- 
parent spots in the thorax of Zilater noctilucus, and the 
subtransparency of the adjoining crust, that the intersti- 
tial substance in this situation has also the property of 
shining—a supposition which, if De Geer and other 
authors be correct in stating that this insect has two 
luminous patches under its elytra, and that the inci- 
sures between the abdominal segments shine when 
stretched, may probably be extended to the whole of the 
interstitial substance of its body.— What peculiar organi- 
zation contributes to the production of light in the hollow 
projections of Fulgora laternaria and candelaria, the 
hollow antennee of Pausus spherocerus, and under the 
whole integument of Scolopendra electrica, Mr. Macart- 
ney was unable to ascertain. Respecting this last he re- 
marks, what I. have myself observed, that there is ‘an 
apparent effusion of a luminous fluid on its surface, that 
may be received upon the hand, which exhibits a phos- 
phoric light for a few seconds afterwards; and that it 
will not shine unless it have been previously exposed for 
a short time to the solar light?. 
® Phil. Trans, 1810, p. 281.—Mr, Macartney’s statement on this 
