The callosities upon the limbs and chest, and the hump on the back, have caused much perplexity among naturalists; but, perhaps, their purpose may be explained. They seem to bear some relation to the necessities of the animal, considered as the slave or man. The callosities are the points on which it kneels down to receive its burden. The hump, which is a fatty secretion, is known to be absorbed into the system when the animal is pinched for food, thus forming a provision against the casualties to which it is subject in a life evidently ordained to be passed in the desert. Add to this, that its singularly formed stomach renders it capable of containing a supply of water suitable to long journeys, and we have ample evidence of the purpose for which this singular and useful creature was designed. The camel furnishes the Arab with flesh and milk, of its hair he weaves clothing, and even tents; his belt and sandals are the produce of its hide, and its dung affords him fuel. The hair of the Persian camel is held in the highest estimation. There are three kinds of it--black, red, and grey; the black being of most value, and the grey fetching only half the price of the red. But all such uses are mere trifles when compared with the value of these animals as beasts of burden--"ships of the desert," as they have been poetically named. By means of them, communication is kept up between distant countries separated by large tracts of frightful deserts, which, without some such aid, would be entirely impassable by man. We arrive at the _Llamas_, or camel sheep, as the old Spanish colonists used to call them. These animals are natives of South America, and their range is limited. They are found only on the high plateaus of the Andes; through which they extend, from New Granada on the north to Chili on the south, though one species ranges even to the Straits of Magellan. In all there are four distinct species of them--the Llama proper, the Paca or Alpaca, the Guanaco, and the Vicuna. The Llama and Paca are both held in a state of domestication; the former as a beast of burden, and the latter for its hair or wool. On the other hand, the Guanacos and Vicunas are wild animals, and are eagerly hunted by the mountain tribes of Indians for their flesh and skins, but in the case of the vicuna for the very fine wool which it yields, and which commands an enormous price in the markets of Peru.