=Foods and mode of digestion.= All kinds of poultry and most of our common wild birds are omnivorous eaters, but the proportion of different foods usually taken is not the same in different kinds of birds. Some eat mostly grains, some mostly animal foods. Some can subsist entirely on grass if they can get it in a tender state; others eat very little grass. The scratching birds like a diet of about equal parts of grain, leaves, and insects. Pigeons and canaries live almost entirely on grains and seeds, but like a little green stuff occasionally. Domestic birds which produce many eggs require special supplies of food containing lime to make the shells. Until within a few years it was universally believed--and it is still commonly supposed--that birds needed grit to take the place of the teeth nature did not give them, and assist in the grinding of the food in the gizzard. Many close observers now reject this idea because they find that birds supplied with digestible mineral foods do not eat those that are not digestible. A bird does not need teeth to grind its food, because it is softened in the crop and the gastric juice acts upon it before the grinding process begins. =Peculiarities of birds' eggs.= The only animal foodstuff produced in a natural package, easily preserved and handled, is the egg. In the vegetable world we have a great many such things--fruits, seeds, roots, nuts, with coverings of various textures to protect the contents from the air. In all of these the material stored up is either for the nourishment of the seeds in the first stages of growth as plants, or for the nourishment of a new or special growth. An egg is the seed of an animal. All animals produce eggs, but in mammals the new life originating from the egg goes through the embryonic stages within the body of the parent, while in insects, fishes, reptiles, and birds the egg is laid by the creature producing it before the embryo begins to develop. In mammals the embryo grows as a part of the body of the parent, the substances which build it up coming from the parent form as they are needed. In birds a tiny germ--the true egg--is put, with all the material needed for its development as an embryo, in a sealed package, which may be taken thousands of miles away from the parent, and, after lying dormant for weeks, may begin to grow as soon as the proper conditions of temperature are applied. The food value of the germ of an egg is inappreciable. We use the egg to get the material stored up in it for the young bird which would come from the germ.