=Reproducing the flock.= Fowls are short-lived creatures. They mature in less than a year; their period of greatest productiveness is usually over before they are two years old, and only a very small proportion of a flock are worth keeping after that. Hence the entire stock of fowls on a farm is renewed in two years. Most farmers intend to kill off all their two-year-old hens each year, thus keeping up the number in the flock by growing annually about as many young birds as there are hens in the flock. To allow for losses, for an excess of males, and for inferior pullets which are not worth keeping for layers, it is necessary to hatch about four times as many chickens as are to be reserved. =The hatching season.= Most of the chickens reared on farms are hatched in the spring months. The late-hatched chickens are nearly all from hens that steal their nests. People on farms do not want late chickens; among so many larger ones a few small birds have very little chance to make good growth. But those who have a place to keep a few early chickens and time to take care of them often set a few hens in the winter. Eggs will hatch at any season of the year, and chickens will grow if they get proper care; but there is a comparatively short season in the spring when eggs hatch better and chickens grow better than at any other time, and the easiest way to get a given number of good chickens that will be full-grown at the beginning of winter is to hatch them in this natural hatching season. This season cannot be exactly defined, because it varies according to latitude and also from year to year according to the weather. Perhaps the best general rule is to have the first chicks hatch when the grass is beginning to grow. To effect this the hens must be set three weeks earlier, when there may be no signs of spring. No one can time hatches to a natural phenomenon of this kind with certainty, but by planning with reference to the advance of spring in a normal season, the first hatches are usually brought very near to the desired time.