A clever plumber of my acquaintance was once called to a large drapery establishment in the West End of London, because the dressmakers at work in one of the rooms were making complaints of an evil smell that haunted the place. So much had they been troubled, indeed, that several of them had been made ill by it. On examining the workroom my friend found everything apparently faultless. It was a large, well-lighted and airy apartment, and he himself was unable to detect anything amiss in the atmosphere. Plans were consulted, but no evidence could be found of any possible source of unpleasant odour. His opinion therefore was, that the ladies were—ladies, that is to say, fanciful, and the matter was dropped. But the ladies were not consenting parties to this opinion, and the complaints continued. More of the assistants fell ill as a consequence, they said, of the smell, so that he was again sent for. On this occasion, it being the height of summer, he called, on his way to the draper’s emporium, at a butcher’s shop, and much to that man’s surprise, asked permission to capture a few of his bluebottle flies. These he took with him to the draper’s, and, the suspected room having been emptied of furniture and occupants, he closed all the windows and doors and released his flies. After waiting patiently for some time, he observed that these amateur detectives of his had all made for one part of the room, where they were settling on the wall. Here he had an opening made, and found hidden behind the plaster an open drain-pipe, old and foul, which had formerly been connected with a lavatory, and had been enclosed and forgotten during some alterations made on the building several years before. The olfactory sense of insects has been credited with perhaps even more wonderful powers than those we have just been writing about. For instance, both Lubbock and Forel have shown that the extraordinary aptitude ants possess for finding their way back to their nest after their peregrinations in the mazy labyrinth of their world depends upon the sense of smell. On their return to the nest they follow the scent left by their own footsteps. This “homing” instinct, or “orientation,” which is found in many species of insects and animals, has long been a matter of interest to scientific naturalists. The subject is, however, much too large for us to enter fully into on the present occasion. Winged insects like bees and wasps manifest also the homing instinct. In their case the return to the nest or hive is effected probably altogether under the guidance of vision. This is what we should expect, as elevation in the air secures for these creatures a wide and unimpeded view of their world. Circumstances are obviously different in the case of ants and other creeping things, whose immediate outlook, like that of four-footed mammals, is circumscribed to an area of but a few inches or feet at the most.