Stevens' Book of the Farm and many other publications describe the similar affliction of sheep by _Œstrus ovis_ but omit to notice the case of the donkey, which I have witnessed several times, but have never seen a horse or pony thus afflicted. There is a fly termed _Œstrus nasalis_, of which the victimised host is uncertain, for Linnæus was mistaken in stating that the larvæ are found in the _fauces_ of "horses, asses, mules, stags, and goats," _entering by the nostril_. The old fanciful dogma that everything existing was actually created "in the beginning," and "for a purpose," was once ardently championed as controverting aggressive Voltairean atheism, but it must be now recognised as an unwarranted assumption, deduced from an orthodox doctrine of "design," which in itself seems acceptably agreeable with the idea of unity, consistency, and perfection in Creation and The Creator. In fact the said "fanciful" dogma never really was an integral part of Christian Catholic doctrine. The house-fly, as we know it, is absolutely the developed product of human insanitation; scientifically and practically it is a new "species" of an old "genus" established by a long course of breeding in man-made environments. [Illustration: Fig. 1. The House-Fly, Female, _Enlarged_.] [Illustration: Fig. 2. The Lesser House-Fly, Male, _Enlarged_.] [Illustration: Fig. 2a. The Stable-Fly, Female, _Enlarged_.] CHAPTER II THE IDENTIFICATION OF THE COMMON HOUSE-FLY Although there are several other kinds of flies which occasionally visit the dwellings of mankind, there is one super-abundant species, _Musca domestica_, to which the name of "house-fly" pre-eminently belongs. In the scientist's discriminating judgment, when viewed microscopically, it differs substantially from others; but it differs very little in general appearance from certain outdoor flies and from one not uncommon indoor smaller companion, _Fannia canicularis_, which is not classified amongst the _Muscidæ_ but amongst the _Anthomyidæ_. This latter has been fitly termed the "lesser House-fly;" it has the same habit of delighting to pester man as much as or more than cattle outdoors. Both these flies join with several others in frequenting stables and cow-sheds.