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Page:Popular Science Monthly Volume 34.djvu/212

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THE POPULAR SCIENCE MONTHLY.

large animal can be properly adapted for Saharan conditions (liability to attack from lions and other great beasts of prey included), unless it combines these three attributes of a soft tread, a swift, swinging gait, and a long neck, enabling it to reach its food above or below, as necessitated by the height of its legs and body. Ostriches, giraffes, and camels alike, all feed to a considerable extent indeed on foliage of trees.

Of all these animals, however, the most purely desert-haunting is the camel itself, and it exhibits, therefore, a few special peculiarities not equally well developed in any other creature. In the first place, desert journeys imply continued privation, or even at times complete absence of food. Now, whenever in the animal kingdom such a necessity frequently arises in the ordinary life-history of a species, natural selection has provided against it by favoring the survival of those individuals which can lay up spare material against the period of famine in their own tissues. A starving sheep, Prof. Huxley well remarks, is as much a carnivore as the lion that would devour it; it subsists strictly upon its own fat and its own muscle, which it slowly unbuilds to use up in the needful action of its heart, its lungs, its limbs, and its internal organs generally. Hence, in hard times, those animals which have the largest reserve-fund of fat at their disposal will survive longest, and species which often encounter hard times learn organically by hereditary experience to supply such a reserve-fund against possible contingencies. Thus the bear and the dormouse go to sleep sleek and plump for the annual hibernation, and wake up mere loose and baggy masses of skin and bone. The zebu and other tropical oxen gather a huge hump of fat between the shoulders in the wet months while grass is plentiful, to serve them as a store of food during the dry season. But in the camel and dromedary this special provision against famine reaches the highest point, and produces the hump or humps on the back—one in the Arabian or African, two in the Bactrian or Indian variety.

Structurally, of course, the humps are nothing—mere lumps of fat, collected under a convenient fold of the skin, and utterly unprovided for in the framework of the skeleton. When the animal is at its best and well fed, they are full and plump, standing up on his back firm and upright; but on a long journey they are gradually absorbed to keep up the fires that work the heart and legs, and in the caravan camels which arrive at the coast, the skin hangs over, an empty bag, upon the creature's flanks, bearing witness to the scarcity of external food during the course of his long, forced march from the interior. A starved small camel in this state of health far more closely resembles a Peruvian llama than any one who has only seen the fine, well-kept beasts in European menageries or zoölogical gardens could readily imagine.