secure the varieties. On the borders of the deserts, where the cultivated land cuts into them, especially in the region of the Nile Valley and the Red Sea, organic life is fairly well developed. The broad valleys in those regions are changed after rains into green meadows, and in January the perennial plants in every mountain-clove and ravine are covered with foliage and flowers; and annuals spring up, affording a luxuriant flora from February till April. Day moths sport themselves, in few species indeed, but in multitudes of individuals. Along with them buzz numerous wasps and flower-visiting beetles, and in the oases the troublesome ants are associated with a series of insects whose larvæ are bred in the water. Dragon-flies appear in multitudes, often swarming like locusts, and miles from the water, and myriads of stinging flies for short periods make the sojourn of Europeans intolerable. The pests of the home are here too, and vermin that make life a burden even to camels.
Scorpions are plenty, both in the oases and the desert proper, and spiders abound at the opening of the rainy season. Especially is this the case with a little purple spider of a velvety sheen, of which, according to Nachtigall, the people of Bournou believe the red velvet of the Western countries is made. Little crustaceans are numerous in the springs, and one species (Artemia oudenyi) occurs so frequently in some of the salt lakes of Fezzan as to serve, with the larvæ of certain flies, as food for the people. Fish are found in the ponds and underground springs; but the last are individuals which have, as Carl Vogt has shown, only casually reached the springs through underground channels from surface waters; for they betray no sign, either in coloring or the structure of their eyes, that they were ever accustomed to constant darkness. Of double interest is a fish living in the hot springs of Tofra and Lafra, in Tunis; first, because it can bear a temperature of 167° Fahr. without injury, and also because it belongs to a genus of which the other species live only in the sea. A few small fresh-water mollusks are found here and there, and land shells of a class which are capable of enduring protracted drought in a passive condition, and reviving when it begins to rain, and thus afford a remarkable example of adaptation to life in the desert. Frogs and salamanders, which do not easily adapt themselves to an arid environment, can not exist under the conditions of life that prevail in the Sahara, not even in the oases. Some reptiles, birds, and mammals fare better there. These vertebrates, in fact, with insects, are the only animal inhabitants of the desert.
Nearly all these animals, from lions and gazelles to locusts, wear the yellow color of the desert sand, verifying the phrase of the Latin poet, "Flavæ, leænece arida nutrix" ("Dry nurse of the tawny lioness"). The weakling is thus protected by a coat that