614 LUMINOUS INSECTS. 
Which of these opinions is the more correct I do not pretend to decide, 
But though the experiments of Mr. Macartney seem fairly to bear him out 
in denying the existence of any ordinary combination of phosphorus in lu- 
minous insects, there exists a contradiction in many of the statements, 
which requires reconciling before final decision can be pronounced, The 
different results obtained by Forster and Spallanzani, who assert that glow- 
worms shine more brilliantly in axygen gas, and by Beckerheim, Dr. Hulme, 
and Sir H. Davy, who could perceive no such effect, may perhaps be 
accounted for by the supposition that in the latter instances the insects 
having been taken more recently, might be less sensible to the stimulus of 
the gas than in the former, in which perhaps their irritability was accumulated 
by a longer abstinence : but it is not so easy to reconcile the experiment of 
Sir H. Davy, who found the light of the glow-worm not to be sensibly 
diminished in hydrogen gas1, with those of Spallanzani and Dr, Hulme, 
who found it to be extinguished by the same gas, as well as by carbonic 
acid, nitrous and sulphuretted hydrogen gases.? Possibly some of these 
contradictory results were occasioned by not adverting to the faculty which 
the living insect possesses of extinguishing its lights at pleasure. At the same 
time, however, it may be here observed, that as this luminous substance 
can be collected in considerable quantities, there can be no difficulty in 
deciding. by chemical analysis whether it is really phosphoric or not; 
and that till this analysis has been made it is premature to build any hy- 
pothesis on the assumption of its being so, or to apply this epithet to it, as 
is so generally done. 
The general use of this singular provision is not much more satisfactorily 
ascertained than itsnature. I have before conjectured — and in an instance 
I then related it seemed to be so—that it may be a means of defence 
against their enemies. In different kinds of insects, however, it may pro- 
bably have a different object. Thus in the lantern-flies (Hu/gora), whose 
light precedes them, it may act the part that their name imports, enabling 
them to discover their prey, and to steer themselves safely in the night. 
In the fire-flies (Z/ater), if we consider the infinite numbers that in certain 
climates and situations present themselves everywhere in the night, it may 
distract the attention of their enemies or alarm them. And in the glow- 
worm—since their light is usually most brilliant in the female ; in some 
species, if not all, present only in the season when the sexes are destined 
to meet, and strikingly more vivid at the very moment when the meeting 
takes place ®—besides the above uses, it is most probably.intended to con- 
duct the sexes to each other. This seems evidently the design in view in 
those species in which, as in the common glow-worm (L. noctiluca), the 
females are apterous. The torch which the wingless female, doomed to 
craw] upon the grass, lights up at the approach of night, is a beacon which 
unerringly guides the vagrant male to her “love-illumined form,” however 
obscure the place of her abode. It has been objected, however, to this 
explanation, that—since both larva and pupa, as De Geer observed *, and 
the males shine as well as the females—the meeting of the sexes can 
scarcely be the object of their luminous provision. But this difficulty 
appears to me easily surmounted, As the light proceeds from a peculiarly 
organised substance, which probably must in part be elaborated in the larva 
1 Phil. Trans, 1810, p. 287. 3 Phil. Trans. 1801, p. 483. 
5 Miiller in Ilig, Dag. iv. 178. 4 iv, 49, 
