_Incubator Cellar._ It is necessary to provide some room in which the incubators can be installed and operated. This may take the form of a cellar, or the incubators may be operated in rooms above the ground. Many of the incubator cellars on duck farms are only partially under ground and not a few of them are built entirely out of ground. The particular size and shape of the cellar or incubator room will, of course, depend upon the number of incubators to be installed and upon their make and shape. Usually these buildings are constructed with rather thick walls so that the temperature of the room will fluctuate less with changes in outside temperature. Provision is also necessary by means of windows or other ventilating devices to provide for good ventilation in the room. The cellars are usually constructed with cement floors as moisture is used freely and wooden floors would rot out quickly. _Incubator Capacity Required._ The aim on commercial duck farms is to hatch all of the eggs produced which are suitable for the purpose. Practically no eggs are sold except the cracked eggs or those which would not give good results in the incubator such as too large or too small eggs. Occasionally, of course, there will be sales of duck eggs in comparatively large lots for incubation purposes where someone is starting a duck farm. Occasionally also duck farmers buy from each other a few eggs for incubation in order to secure new blood. On the whole, however, practically all of the eggs laid are incubated and it is necessary to have an incubator capacity sufficient to take care of the eggs as they are produced during the flush season. Since the egg production at this time will run around about 80% and since the period of incubation is 28 days and a couple more days must be allowed to take the ducklings out of the machines and to clean up the machines, it is necessary to figure on 30 days between hatches. To take care of the flush production at this time there would be required an incubator capacity of from 20 to 25 eggs per head of breeding ducks. The latter figure is a safer estimate than the former. Of course, eggs sufficient to fill the entire incubator capacity are not put in the machines at any one time but different lots are put in as soon as a sufficient number is obtained to make it worth while. There will be, therefore, eggs in various stages of incubation in different sections of the machines at the same time. While Pekin duck eggs will run about 1/2 heavier in weight than hens' eggs they do not take up a proportionately greater amount of space in the incubator. An incubator tray will accommodate about 5/6 as many Pekin duck eggs as it will hens' eggs.