LUMINOUS INSECTS. 419 



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 Elater 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 incisures 

 between the abdominal segments shine when stretched, 

 may probably be extended to the "iXihole of the interstitial 

 substance of its body. — What peculiar organization con- 

 tributes to the production of light in the hollow pro- 

 jections of Fidgora laternaria and canddaria^ the hollow 

 antennae of Pausus sphccroceruSi and under the whole m- 

 tegument of Geophilus electrims, 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 exhibits 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 light ^. 



=* Phil. Trans. 1810, p. 281.— Mr. Macartney's statement on tliis 

 point is not very clear. He probably means that the insect will not 

 shine in a dark place in the da?/ lime, unless previous]}' exposed to 

 the solar light : for it is often seen to shine at night when it could 

 have had no recent exposure to the sun. 



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