position later. Finally the six holes
are filled with sand which is beaten down so that all is firm. When the
surface is perfectly level, and everywhere the same, except for the six
straws, which mean nothing to the insect, I release my beetles, covering
them with a wire-gauze cover. They are eight in number.

At first I see nothing but the inevitable fatigue due to the incidents
of exhumation, transport, and confinement in a strange place. My exiles
try to escape: they climb the wire walls, and finally all take to earth
at the edge of their enclosure. Night comes, and all is quiet. Two hours
later I pay my prisoners a last visit. Three are still buried under a
thin layer of sand. The other five have sunk each a vertical well at the
very foot of the straws which indicate the position of the buried fungi.
Next morning the sixth straw has its burrow like the rest.

It is time to see what is happening underground. The sand is
methodically removed in vertical slices. At the bottom of each burrow is
a Bolboceras engaged in eating its truffle.

Let us repeat the experiment with the partly eaten fungi. The result is
the same. In one short night the food is divined under its covering of
sand and attained by means of a burrow which descends as straight as a
plumb-line to the point where the fungus lies. There has been no
hesitation, no trial excavations which have nearly discovered the object
of search. This is proved by the surface of the soil, which is
everywhere just as I left it when smoothing it down. The insect could
not make more directly for the objective if guided by the sense of
sight; it digs always at the foot of the straw, my private sign. The
truffle-dog, sniffing the ground in search of truffles, hardly attains
this degree of precision.

Does the _Hydnocystis_ possess a very keen odour, such as we should
expect to give an unmistakable warning to the senses of the consumer? By
no means. To our own sense of smell it is a neutral sort of object, with
no appreciable scent whatever. A little pebble taken from the soil would
affect our senses quite as strongly with its vague savour of fresh
earth. As a finder of underground fungi the Bolboceras is the rival of
the dog. It would be the superior of the dog if it could generalise; it
is, however, a rigid specialist, recognising nothing but the
_Hydnocystis_. No other fungus, to my knowledge, either attracts it or
induces it to dig.[6]

Both dog and beetle are very ne