The "House-fly" is a fit subject for a simplified study of this kind, and the present booklet is an attempt to afford information very different to that of the "popular" works, which only were accessible to the writer's hands between fifty and sixty years ago; the writers of those old books all followed the lead of the reverend and learned contributors to the famous and monumental "Bridgwater Treatises." "The Wonders of Nature explained," "Humble Creatures" (a study of the earth-worm and the house-fly, in popularised language), "The Treasury of Knowledge," "Simple Lessons for Home Use," were the kind of cheaper works in touch with a past generation; these latter and other later well-intended publications will now be found to be somewhat deficient or even a little misleading entomologically; they abounded in pious sentimentality and mostly attempted an aggravatingly grandiose literary style, but all have rather failed in teaching practical economic utility, in connection with which nature-knowledge can be rendered as interesting as any other kind of instructive literature. The tribe of two-winged flies, in particular, has not even yet received a full and adequate study by scientists. A preference has ever been shown towards those other branches of entomology, which may be more interesting to the cabinet-specimen collector, but which cannot pretend to have an equal hygienic and economic importance to humanity. The presence of the house-fly in our dwellings is often submitted to as an irritating but an inevitable nuisance; yet very certain remedial measures would almost exterminate the creature, which is a dangerous and filthy peril. To many people it will seem a most incredible exaggeration when told that it is really worse than any one of the less common creatures universally regarded with horror and disgust as pestiferous vermin. The surmise may be true that the disgusting body louse carried bacteria, which spread the "black death"; and, even though the rat's flea has been found to be the carrier transmitting bubonic plague, yet amongst people living now in civilised communities within the temperate zones these parasites cannot be ranked as dangerous equally with the house-fly. The modern crusade against the house-fly is not based on any such new discovery, as is that against the mosquito gnats, which are the means of spreading zymotic diseases mainly in the tropics. The malignity of the fly is recorded in most ancient history and folk-lore, yet not very long ago there prevailed amongst certain classes opinions very different to those of old as well as to those of the present day. A short anecdote will perhaps amuse as well as explain those misplaced sentiments, which have not quite died out.