When you take him for a walk also, how busy his nose makes him! Burrowing here and there among the grass and undergrowth, picking up an interesting trail that leads him a little way, until it crosses another, fresher, perhaps, or more interesting, that has to be taken up—here a cat’s, there a rat’s, further on a rabbit’s, and then, with short squeals, scrapings in the ground, and buryings of his muzzle, a weasel’s!—the whole intermixed and intermingled with whiffs of something like old decayed bones, or of another and an unfriendly dog, or of some ardent lady-love who has passed this way but shortly since!—is not this a richer, a fuller, a more attractive, world than ours, with its fickle sunlight, its pallid greys, its mournful purples, its unattainable horizon-blue? For our life is primarily one of vision. I am sure his dreams, also, are compounded of the gorgeous odours of some other world, such odours as even our woods in autumn know nothing of. But we must return again to science and Fabre. This time we shall accompany him on an excursion with the wonderful dog who is trained to discover for the _gourmet_ the truffles that are growing deep in the soil. Left to his own devices, we learn, the truffle-hunting dog indicates the position not only of truffles, but also of all manner of hypogean (underground) fungi, “the large and the small, the fresh and the putrid, the scented and the unscented, the fragrant and the stinking.” Only, he never at any time indicates the presence of the ordinary mushroom, not even while it is still underground, before it sprouts up as the fungus we know. And yet to our nostrils the mushroom has the same smell as many of the hypogean fungi he does indicate. Consequently, therefore, the dog is not guided to the deep fungi by what may be called the general odour common to all fungi. He must be able, that is to say, to distinguish the hypogean varieties by some quality which is not odour, or, at least, not odour as we understand it. There is, as it happens, something like a truffle-hunter among the insects also, what is known as the Bolboceros beetle. This little creature feeds on the _hydnocystis arenaria_, a hypogean fungus. Fabre, having captured some of these insects, placed them on earth in which he had buried the fungus at depths of six or seven inches. It was found that the beetles, without making any trial bores, sank vertical shafts through the soil direct to their food. We may insert here also, as bearing upon the problem which is now emerging into clearness, an observation and a suggestion similar, as we shall see, to that of Fabre, on the badger by Mr. Douglas Gordon (_Spectator_, August 6th, 1921):