_Age of Hatching Eggs._ Duck eggs should be set as often as enough are secured to fill one or more trays in the incubator or enough to produce a sufficient number of ducklings to utilize brooding space to advantage. Since duck eggs deteriorate more rapidly than hens' eggs they cannot be kept so long before they are set. It is best not to save them for longer than one week. During the season of flush production it is not, of course, necessary to save them that long since enough eggs will be secured to set each day if desired. The usual practice at this time is to set twice a week. During the early part of the season when the production of eggs is low and the temperature cool the eggs are often saved for as long a period as two weeks without noticeably bad results. _Care of Hatching Eggs._ Eggs for hatching should be kept in a cool place. Any place suitable for keeping hens' eggs for hatching is a suitable place for duck eggs. The temperature should be from 50 deg. to 70 deg. Fahrenheit. Where the eggs are not kept longer than one week, it is not necessary to turn them, especially if they are kept on end. If kept longer than this it is safer to turn them once a day or once in two days, handling them carefully so as not to crack any or to injure their hatching qualities. _Selecting the Eggs for Hatching._ Medium sized eggs are preferred for this purpose. Therefore, the extremely large eggs and the very small ones are thrown out. Rough shelled eggs or eggs with crooked or deformed shells are likewise thrown out since they are not likely to hatch well. Eggs that are badly soiled so that they cannot be tested easily are washed but the clean eggs are not. All the eggs intended for incubation purposes are sounded by striking them gently against one another in order to detect and remove the cracked eggs. No selection is made on the basis of color. The eggs may be white, creamy white or a blue, or bluish green in color. At the present time a considerably less proportion of the eggs show a blue tint than formerly. As the egg laying season advances the eggs laid by the ducks tend to get a little larger. _Temperature._ Up to the time of testing, that is, about the fifth day, the incubator is run at a temperature of from 101 to 102 degrees. After the fifth day the temperature is kept as near 103 as possible. The most sensitive period for a duck egg is during the first 3 or 4 days of incubation. If they are allowed to get too warm during this time the germ may be killed while if the temperature is too low, development will be retarded.