PHOSPHORIC INSECTS. 149 
the yellow greasy tissue of the spots im the thorax 
of H. 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 hght shone between the segments 
of the abdomen when these were separated one 
from another. 
Morren, late Professor of Botany in the Uni- 
versity of Liége, 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 extmeguished, 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 (later) is more brilliant 
when the insects are flying, for then their spira- 
* JT have not read M. Morren’s paper. It is abridged in Kirby 
and Spence’s Introd. to Ent. p. 513 (edit. in one vol.). 
