In suitable places in warm weather the eggs will hatch in from eight to twelve hours and the larvæ will become fully developed in from eight to fourteen days. They then change to pupæ (Fig. 50) in which stage they may remain for another eight to twenty days when the adult flies will emerge. These figures must necessarily be indefinite because the weather and other conditions always vary. Under the most favorable conditions of moisture and temperature it is probably never less than eight days from egg to adult fly and under unfavorable conditions it may be as long as six weeks. The larvæ thrive best when the manure is kept quite wet. I have often found them in almost incredible numbers in stables that had not been cleaned for some time. The horses standing there at night added fresh material and kept it just wet enough to make conditions almost ideal (Fig. 49). The pupæ are usually found where the manure is a little dryer, but it must not be too dry. When the flies issue from the pupæ they push their way up to the surface where they remain for a short time and allow the body to harden and the wings to dry before they fly away to other manure or, as too often happens, to some near-by kitchen or restaurant or market place. [Illustration: FIG. 48--Barn-yard filled with manure. Millions of flies were breeding here and infesting all the near-by houses.] [Illustration: FIG. 49--Dirty stalls; the manure had not been removed for some days and the floor was covered with maggots.] Of course it is impossible for them to issue from this filth without more or less of it clinging to their bodies. Now if these flies would breed only in barn-yard manure and fly directly from the stable to the house there would be comparatively little reason to complain, at least from a sanitary standpoint, for the amount of barn-yard filth that they carried to our food would be of little consequence. But when they breed in privy vaults or similar places, or visit such places before coming into the house or dairy or market place the results may be much more serious. FLIES AND TYPHOID