If any one of the above suppositions be true, it does not exclude any other one, amongst many explanatory surmises, from being possible. Judging from the remarkable attractiveness of the odour of humanity to the common house-fly, and from the fact of the maggots possessing well developed tenter-hooks on their heads (somewhat like those which the bot-fly maggots use for internal attachment), it is just as likely, nay more likely, that this species (as the writer stated for the information of the authorities of Westminster Hospital nearly fifty years ago) is more than any other capable of adopting such a life-cycle existence; these maggots would mature after five or six days feeding and then emerge. If there were a veritable "_Œstrus hominis_," however rare, the hairy and peculiar female would be conspicuously observable, a persistent hoverer about the person of her victim until she had attached eggs to his body, from which the maggots would not emerge until after nine months. Most of the tropical flies, which are said to similarly attack humanity, may be rather compared to the green-bottle flies which infest sheep, but the latest medical records and reports profess to identify ten or twelve species of very different genera as having myiasic capabilities. The family of _Œstrida_ has been fitly divided into three sections, namely, the _Gastrophilinæ_ (the larvæ living in the gullet, the stomach, or the intestines), the _Hypoderminæ_ (worble-flies), and the _Œstrinæ_ (nasal or nostril flies); all the species are hairy or furry, and the gravid females fly slowly with loud buzzing, in a characteristic attitude peculiar by the bending downwards of abdomen and tail, with a much extruded ovipositor. The sheep's nostril-fly, _Œstrus ovis_, has a chequered abdomen and is less hairy than others; it is the type of the section to which the generic term _Cephalomyia_ is given in some books; species of this section attack deer and other animals. The section termed _Hypoderminæ_ comprises the "worble" flies or "marble" flies. One may imagine that the latter name indicates in the mind of the cowherd the appearance of the round pustulent boils on the hide of the suffering animal, and that the former name is a corruption of "worm-hole," originating with the tanner, observant of the deterioration of injured hides. A mixing of the terms worm-hole and marble probably originated the name "warble." The maggots live under the skin on the back of oxen, and breathe externally through openings in the boil-like excrescences. The discoloured flesh of infected oxen is called "flecked." Two species of worble-flies are prevalent, one or the other, in many parts of England. The third section, to which the sub-family termed _Gastrophilina_ is sometimes applied, comprises the "bot-fly," which commonly infects the horse; it is the imperfect knowledge of this latter which has led to erroneous surmises explanatory of the horribly disgusting fact of human intestinal myiasis.