Investigating the orientation of ants, Forel found, first of all, that while the covering of their eyes with an opaque varnish “embarrassed” them to some extent, they went hopelessly astray when their antennæ were removed. He also repeated Lubbock’s well-known experiments of supplying the ants with bridges over obstacles in the neighbourhood of their nests, noting their behaviour when the bridges were changed, removed, or reversed, with the result that he came to credit the olfactory system of ants with much greater powers than the more cautious Lubbock would have believed. These insects, says Forel, exploring with their mobile antennæ the fields of odour they encounter, form in their memory a kind of “chemical topography.” Thus when an ant sets out from her nest she distinguishes the various odours and varying strengths of odours she comes upon, noting and memorising them as in two main fields, one on her left side, the other on her right. In order to find her way back again all she has to do is to unwind, so to speak, the roll in her memory, transposing right and left, and this successfully accomplished will bring her back to the point she started from. If, he concludes, we ourselves were endowed with such a perfect olfactory mechanism situated in long, flexible whip-lashes, which we could move and tap with each step, the world for us would be transformed. Odour would become a sense of forms. Thus the orientation of ants can be explained without assuming the existence of an unknown sense. (It has recently been suggested, by the way, that bats owe the exquisite power they manifest of steering their flight among obstacles to the use of their squeaks, the echoes from which enable them to form “sound-pictures” of their environment. In the same way a blind man in the street tapping the pavement with his stick forms a more or less well-defined sound-picture of the walls, doorways, and alleys about him.) In the immediately foregoing paragraphs we have been dealing with the ability of insects to smell the smells that we smell. But Fabre’s experiments have familiarised us also with the notion that there are insects which can smell smells we cannot smell. We shall see in the following section that the same may also be true of some of the higher animals. In fish olfaction is, unlike that of air-breathing animals, effected by odorous material in solution. Whether or not their olfactory sense is as acute it is impossible in the present state of our knowledge to say. Anatomically the end-organ of fishes is simpler, but there are some species, the dog-fishes for example, which possess a large olfactory lobe in the brain; and this certainly suggests that they, at all events, are gifted with an olfactory sense of relatively high development.