424 LUMINOUS INSECTS, 



the adjoining luminous substance, which it has the 

 power of voluntarily extinguishing, not by retracting" 

 it under a membrane, as Carradori imagined, but by 

 some inscrutable change dependent upon its will : and 

 when the latter substance was extracted from living 

 glow-worms it aflbrded no light, while the two sacs in 

 like circumstances shone uninterruptedly for several 

 hours. Mr. Macartney conceives, from the radiated 

 structure of the interstitial substance surrounding the 

 oval yellow masses immediately under the transparent 

 spots in the thorax of Elater noctilucus, and the sub- 

 transparency 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 wliole of 

 the interstitial substance of its body. — What peculiar 

 organization contributes to the production of light in 

 the hollow projections of Fulgora laternaria and cande- 

 laria, the hollow antennas of Pausus sphcerocerus, and 

 under the whole integument of Scolopendra electrica, 

 Mr. Macartney was unable to ascertain. Respecting 

 this last he remarks, 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 ex- 

 hibits a phosphoric 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 lights 



' P/iil. Trans. 1810, p. 281. — Mr. Macartney's statement on tliis point 

 is not very clear, lie piobiibly means that the insect will not shine in a 



