30 FORM AND HABIT: THE BILL. these birds are largely ground-haunters, and most of them inhabit regions where the snowfall is heavy, the toes in winter acquire a comblike fringe on either side. Practi- cally, therefore. Grouse don snowshoes in the fall, and wear them until the following spring. The Bill. — Of the four organs we are considering, the bill is beyond question the most important. We have seen that a bird may be wingless and practically tailless, and may almost lose the use of its feet ; but from the moment the bill breaks the eggshell and liberates the chick, the bird's life is dependent upon its services. The variety of offices performed by the bill, and the correspondingly numerous forms it assumes, are, doubtless, without parallel in the animal world. The special modification of the fore limbs as flight- organs deprives birds of their use for other important services, and consequently we have a biped which, so far as their assistance goes, is without arms or hands. As a result, the duties which would naturally fall to these members are performed by the bill, whose chief office, therefore, is that of a hand. Occasionally it is sexually adorned, as in the Puffins, several Auks, Ducks, and the White Pelicans, which, during the nesting season, have some special plate, knob, or color on the bill. With the Woodpeckers it is a musical instrument — the drumstick with which they beat a tattoo on some resounding limb. Owls and some other birds, when angry or frightened, snap their mandibles together like castanets. But it is as a hand that the bill gives best evidence of adaptation to or by habit. Among families in which the wings, tail, and feet are essentially alike in form, the bill may present great vari- ation — proof apparently of its response to the demands made upon it. All birds use it as a comb and brush ^vith which to
