st be
guided towards their object mainly if not exclusively by the sense of
smell; but that which excites astonishment is the small degree of odour
which seems to suffice for the purpose; the subtlety and rapidity with
which it traverses and impregnates the air; and the keen and quick
perception with which it is taken up by the organs of those creatures.
The instance of the scavenger beetles has been already alluded to; the
promptitude with which they discern the existence of matter suited to
their purposes, and the speed with which they hurry to it from all
directions; often from distances as extraordinary, proportionably, as
those traversed by the eye of the vulture. In the instance of the dying
elephant referred to above, life was barely extinct when the flies, of
which not one was visible but a moment before, arrived in clouds and
blackened the body by their multitude; scarcely an instant was allowed
to elapse for the commencement of decomposition; no odour of
putrefaction could be discerned by us who stood close by; yet some
peculiar smell of mortality, simultaneously with parting breath, must
have summoned them to the feast. Ants exhibit an instinct equally
surprising. I have sometimes covered up a particle of refined sugar with
paper on the centre of a polished table; and counted the number of
minutes which would elapse before it was fastened on by the small black
ants of Ceylon, and a line formed to lower it safely to the floor. Here
was a substance which, to our apprehension at least, is altogether
inodorous, and yet the quick sense of smell must have been the only
conductor of the ants. It has been observed of those fishes which travel
overland on the evaporation of the ponds in which they live, that they
invariably march in the direction of the nearest water, and even when
captured, and placed on the floor of a room, their efforts to escape are
always made towards the same point. Is the sense of smell sufficient to
account for this display of instinct in them? or is it aided by special
organs in the case of the others? Dr. MCGEE, formerly of the Royal Navy,
writing to me on the subject of the instant appearance of flies in the
vicinity of dead bodies, says: "In warm climates they do not wait for
death to invite them to the banquet. In Jamaica I have again and again
seen them settle on a patient, and hardly to be driven away by the
nurse, the patient himself saying. 'Here are these flies coming to eat
me ere I