er, the essential object of his
search, possesses a fairly vivid odour.

But what are we to say of the Great Peacock moth and the Oak Eggar, both
of which find their captive female? They come from the confines of the
horizon. What do they perceive at that distance? Is it really an odour
such as we perceive and understand? I cannot bring myself to believe it.

The dog finds the truffle by smelling the earth quite close to the
tuber; but he finds his master at great distances by following his
footsteps, which he recognises by their scent. Yet can he find the
truffle at a hundred yards? or his master, in the complete absence of a
trail? No. With all his fineness of scent, the dog is incapable of such
feats as are realised by the moth, which is embarrassed neither by
distance nor the absence of a trail.

It is admitted that odour, such as affects our olfactory sense, consists
of molecules emanating from the body whose odour is perceived. The
odorous material becomes diffused through the air to which it
communicates its agreeable or disagreeable aroma. Odour and taste are to
a certain extent the same; in both there is contact between the material
particles causing the impression and the sensitive papillae affected by
the impression.

That the Serpent Arum should elaborate a powerful essence which
impregnates the atmosphere and makes it noisome is perfectly simple and
comprehensible. Thus the Dermestes and Saprinidae, those lovers of
corpse-like odours, are warned by molecular diffusion. In the same way
the putrid frog emits and disseminates around it atoms of putrescence
which travel to a considerable distance and so attract and delight the
Necrophorus, the carrion-beetle.

But in the case of the Great Peacock or the Oak Eggar, what molecules
are actually disengaged? None, according to our sense of smell. And yet
this lure, to which the males hasten so speedily, must saturate with its
molecules an enormous hemisphere of air--a hemisphere some miles in
diameter! What the atrocious fetor of the Arum cannot do the absence of
odour accomplishes! However divisible matter may be, the mind refuses
such conclusions. It would be to redden a lake with a grain of carmine;
to fill space with a mere nothing.

Moreover, where my laboratory was previously saturated with powerful
odours which should have overcome and annihilated any particularly
delicate effluvium, the male moths arrived without the least indication
of confusion or d