This is the way in which robins and sparrows and other birds are born.—The dog, the elephant, the mouse, and the other four-legged animals grow from eggs but
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Photograph by Eugene J. Hall.
they do not grow in the ground or in the water. They grow up in the nest but the nest is not in the trees or in the bushes or in the grass. It is in the body of the mother. When the egg leaves the ovary it does not pass out of the mother. It goes close by into a little bag, called the uterus. The uterus is the nest in which the egg grows
