The originating germ somehow at some time must be supposed to have effected a lodgment in the body of the fly or possibly that of the maggot. Later on, one cannot say when, fungic spawn (a pulpous mycelium) starts a course of development, invades every part of the body, quickly kills the fly, and fixes it to the spot to which in its last moments it has crawled, often a window-pane. Its corpse is now swollen with the spawn developed into masses termed hyphal; but these should not be called hyphal (thread) but quasi-sclerotia, bodies intermediate in a process of normal development between the mycelium and the fruiting stage; fungic fructification ensues with great rapidity; and the corpse becomes suffused with an appearance of white mouldy excrescences, filiform conidiophores, of which the club-like tips make a copious ærial discharge of white spores; when these adhere to a glass or window-pane they imprint thereon a remarkable halo. Attempts to artificially infect other flies with these spores are common failures or have led to contrary conclusions. The period from the first symptoms of distress to the death of the fly, and from that time to the spore discharge is wonderfully short. The infectious germs may have been long dormant in the fly, and very likely may have been acquired in the maggot stage. In the absence of exact knowledge, we can only make conjectures from observations of some kindred fungic parasites, which are not very uncommon amongst the chrysalids of certain moths, beetles, and the pupæ of some annual wild bees. In these cases it seems very unlikely that the infection was incurred otherwise than in the caterpillar or larval feeding stage. Dampness and insanitary conditions seem to favour the spreading of such disease, especially amongst artificially reared larvæ when crowded together and closely confined. Other kinds of flies do not, so often as the house-fly, perish from _Empusa muscæ_, but I have seen a common yellow cowdung-fly, as early as June, thus affected. In spite of all antagonists the brood of the house-fly flourishes and multiplies, but this is because great opportunity and encouragement is provided by the neglect of good sanitation by mankind. CHAPTER IX DISSEMINATORS OF DISEASE The house-fly may seem at first much less to be dreaded than any one of the painfully "biting" or (to be correct) skin-piercing and blood-sucking flies; yet it should be regarded as a much greater enemy to humanity and a more dangerous peril than any of those other flies, of which some short mention and description has now been given. Its life-history and its fecundity have been already alluded to; its rapid growth and maturity counterbalance the fact that it is short lived.