Like nearly all the large land animals, the musk-ox is of gregarious habit, and maintains itself in herds of small size, usually not exceeding thirty or forty head. Its sharp, down-dropping horns seem to have been specially designed by nature to puncture the hide of the big white arctic wolf, which seeks big game at its farthest north. Whenever a musk-ox herd is attacked by wolves, or by dogs, the adult bulls and cows immediately form themselves into a hollow circle, with the calves inside; and thus they stand literally shoulder to shoulder, facing outward with horns at the “ready,” quite able to repel all attacks save those with firearms. If a dog or wolf comes near enough to a musk-ox so that there appears to be a chance to impale it, out rushes the musk-ox in a swift charge. Usually the nimble footed canine escapes unharmed, and as soon as it is beyond reach the musk-ox quickly returns to his place in the circle. The definiteness and precision with which the charge is made and the return accomplished shows a high degree of strategic intelligence; and thus is the fittest enabled to survive. The musk-ox has two coats of hair--a sweater and a rain-coat. The sweater is of fine and dense fur, practically impervious to cold. The rain-coat is a suit of rather long and rather coarse straight hair, which hangs over and completely covers the inner coat, for the purpose of shedding snow and rain. The body color of the animal is a rich chocolate brown, and the legs are dull gray. Naturally one would expect to see a musk-ox provided with a broad, spreading hoof, like the snow-shoe hoof of the caribou; but this is not the case. The musk-ox hoof is rather small and compact. Structurally this remarkable animal is half ox and half sheep,--just as its generic name, _Ovibos_, implies. It has _no_ visible tail, and its drooping horns strongly resemble those of the Cape buffalo, of Africa. For four years the New York Zoological Park has maintained the only herd of musk-ox ever kept in captivity. It started in 1910 with six animals, three of which still survive. SUPPLEMENTARY READING [Illustration: A MUSK-OX] THE AMERICAN NATURAL HISTORY _By W. T. Hornaday_ OUR VANISHING WILD LIFE _By W. T. Hornaday_ FOUR-FOOTED AMERICANS AND THEIR KIN _By M. Wright_ BIG GAME OF NORTH AMERICA _By G. O. Shields_ OUR BIG GAME _By D. W. Huntington_ ⁂ Information concerning the above books and articles may be had on application to the Editor of The Mentor. THE OPEN LETTER