PHOSPHORIC INSECTS. 149 



the yellow greasy tissue of the spots in the thorax 

 of E. noctilucus can be communicated, it appears, 

 to the interstitial tissue which pervades the whole 

 of the insect's body. It was De Geer who first 

 observed that light shone between the segments 

 of the abdomen when these were separated one 

 from another. 



Morren, late Professor of Botany in the Uni- 

 versity of Liege, has studied minutely the struc- 

 ture of the luminous organ of Lampyris noctiluca.* 

 He has shown that the luminous sacs described 

 by Macartney are connected with a multitude of 

 trachean ramifications (air-tubes), and that the 

 luminous property of the glowworm appears to 

 depend, to a considerable degree, upon the pro- 

 cess of respiration. The trachean ramifications 

 proceed from a large trachea which issues from a 

 spiracle (breathing-hole) situated immediately at 

 the side of the luminous mass, on the exterior of 

 the insect's body. When this spiracle is closed 

 the light is immediately extinguished, and reap- 

 pears when the spiracle is opened. As insects 

 have the power of opening or closing their spira- 

 cles at will, the glowworm can thus increase or 

 diminish its light. This also explains why the 

 light of the fire-flies (Elater) is more brilliant 

 when the insects are flying, for then their spira- 



* I have not read M. Morren's paper. It is abridged in Kirby 

 and Spence's Introd. to Ent. p. 513 (edit, in one vol.). 



