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the adult organ seen in an early stage of their growth. The 
capsule was pierced at one place by a tracheal tube. The 
organ of the larva is, though rudimentary in size and function, 
essentially of similar structure to that of the adult female. 
The Wurzburg Professor appears to have been the first 
author who laid special stress on the anatomical arrangement 
and nerve character of the light- organ. Macartney (in Phil. 
Trans. 1810) says, “ The light proceeds from masses of a 
substance not generally differing , excepting in its yellow (?) 
colour, from the interstitial fatty substance of the rest of 
the body ; " and again, “ In the glowworm, besides the last- 
mentioned substance (which, when the season for giving light 
is passed, is absorbed, and replaced by the common interstitial 
substance), there are to be seen on the inner side of the last 
abdominal segment two minute oval sacs, formed of an elastic 
spirally-wound fibre, similar to that of tracheae, containing a 
soft yellow substance of a closer texture than that which lines 
the adjoining parts, and affording a more permanent and 
brilliant light. This light Macartney found to be less under 
control of the insect than that from the adjoining substance, 
which it has the power of voluntarily extinguishing by some 
change dependant on its will. When the latter substance was 
extracted from living glowworms it afforded no light, while the 
two sacs in like circumstances shine uninterruptedly for 
several hours. Macartney conceives, however, that the inter- 
stitial substance has the property of shining ( Kirby 8f Spence, 
vol.,2). 
This account of Macartney's does not appear to be a for- 
tunate one. The two small light-organs of the last segment 
are but an inconsiderable part of the whole light apparatus of 
the female, the larger masses of which have been confounded 
with the “ common interstitial substance." The cell nature of 
the parenchyma of the light-organs has been satisfactorily 
demonstrated by Kolliker, as also the albuminous character of 
their contents. The common interstitial substance is, on the 
contrary, composed of fatty matter, inclosed in a membranous 
envelope. The essential difference in anatomical structure and 
chemical constitution is therefore beyond question. Moreover, 
the light, however produced, emanates from the pale cells of 
the light- organs. But this light, like that of the sun, is 
reflected and refracted in passing from one medium to another 
of greater or less density. The parenchyma cells, which con- 
tain granules and minute crystals of urates, act as refracting 
and reflecting bodies ; and the fatty refractive matter of the 
common interstitial substance contributes further to the 
general illumination by its physical properties. The light 
emitted by the true organs from as many distinct points or 
