fowls and of ducks is not great enough to account for the difference in resistance to the penetration of water. The peculiar quality of the plumage of swimming birds is its density. If you take up a fowl and examine the plumage you will find that it is easy to part the feathers so that the skin can be seen. It may be done with the fingers, or even by blowing gently among the feathers with the mouth. Now try to separate the feathers of a duck so that the skin will be visible. You find it much harder, because the feathers are so thick and soft and at the same time so elastic. The familiar phrase "like water from a duck's back" is not especially appropriate. The feathers on the back of most birds are a very effective protection against rain. The feathers all over a duck are such poor conductors of water that it is hard to remove them by scalding. The structure of the plumage of swimming birds adds to their buoyancy in the water. They do not have to exert themselves to remain on the surface, but float like cork.

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.

Development of the egg. The method of the formation of an egg is very interesting. It is the same in all birds, but is most conveniently studied in fowls. If a laying hen is killed and the body is opened so that the internal organs can all be seen, one of the most conspicuous of these is a large, convoluted duct having its outlet at the vent. In this duct, which is called the oviduct, are eggs in various stages of formation. At its upper extremity, attached to the backbone, is a bunch of globular yellow substances which are at once identified as yolks of eggs in all sizes. The organ to which these are attached is the ovary. The smallest yolks are so small that they cannot be seen without a powerful microscope. These yolks are not germs, but as they grow the germ forms on one side of each yolk, where it appears as a small white spot.

When a yolk is full-grown it drops into the funnel-shaped mouth of the oviduct. Here it is inclosed in a membranous covering, called the chalazæ, and receives a coating of thick albumen. The function of the chalazæ is to keep the yolk suspended in the center of the egg. It does not merely inclose the yolk, but, twisted into cords, extends from either end and is attached to the outer membrane at the end of the egg.

After leaving the funnel the egg passes into a narrow part of the oviduct, called the isthmus, where it receives the membranous coverings which are found just inside the shell. From the isthmus it goes into the lowest part of the oviduct—the uterus. Here the shell is formed, and at the same time a thin albumen enters through the pores of the shell and the shell membranes and dilutes the thick albumen first deposited. After this process is completed the egg may be retained in the oviduct for some time. It is, however, usually laid within a few hours.

Rate and amount of egg production. In the wild state a bird, if not molested after it begins laying, produces a number of eggs varying in different kinds, according to the number of young that can be cared for, and then incubates them. If its first eggs are removed or destroyed, the bird lays more, usually changing the location of its nest. In domestication the eggs of most kinds of birds are removed from the nests daily as laid, and the birds lay many more eggs before they stop to incubate than they do in the wild state.

It is, and has been for ages, the common opinion that the wild birds and poultry, when first domesticated, were capable of laying only a small number of eggs each season, and that laying capacity has been enormously increased in domestication; but the oldest reports that we have of the amount of egg production indicate that the laying capacity of fowls was as great centuries ago as it is at the present time. Recent observations on wild birds in captivity show that even birds which pair and usually lay only a few eggs each season have a laying capacity at least equal to the ordinary production of hens. Quails in captivity have been known to lay about one hundred eggs in a season, and an English sparrow from which the eggs were taken as laid produced over sixty.

The constitutional capacity to produce ovules is now known to be far greater than the power of any bird to supply the material for the nourishment of germs through the embryonic stage. The principal factors in large egg production are abundance of food and great capacity for digesting and assimilating it.

Incubation. A bird before beginning to lay makes a nest. Some birds build very elaborate and curious nests; others merely put together a few sticks, or hollow out a little place on the ground. In birds that pair, the male and female work together to build the nest. Even in polygamous domestic birds like the fowl and the duck, a male will often make a nest for the females of his family and coax them to it as a cock pigeon does his mate.

If the birds are left to themselves and the eggs are not molested, an aërial bird will usually lay a number of eggs equal to the number of young the parents can feed as long as they require this attention, while a terrestrial or aquatic bird will usually lay as many eggs as she can cover. The desired number of eggs having been laid, the process of