The male mounts the hen from behind and stands on her back. The rooster's cloaca transfers semen into the cloaca of the hen. The cloaca is a common receptacle for the intestinal tract, the reproductive system and the urinary system. A spermatozoa sac makes its way up the oviduct and is stored in accessory sex organ in the female. There, the sperm is nourished and released over several days. So the rooster does not have to mate with the hen each time she lays an egg to produce a fertile egg. Fertility only remains high for about 10 days before another mating is needed to increase fertility of the eggs laid. Egg yolks that have a germ cell on the surface are ovulated about every 24 to 26 hours. The spermatozoa fertilize the germ cell, then the albumen, or white of the egg is secreted around the yolk by the reproductive tract. Then the shell membranes and the shell are secreted and deposited as the egg travels down the reproductive tract. The egg is laid back through the cloaca, as mentioned above. This is the way fertile eggs are laid by the hen. The hen would still lay eggs if a rooster were not around, but the eggs would not be fertile.