248 THE POPULAR SCIENCE MONTHLY. 



secure the varieties. On the borders of the deserts, where the cul- 

 tivated 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 mount- 

 ain-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 trouble- 

 some ants are associated with a series of insects whose larvae 

 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 larvse 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 struct- 

 ure 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 tempera- 

 ture 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 des- 

 ert. 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, " Flavce, lecenece arida nutrix " (" Dry nurse of the 

 tawny lioness"). The weakling is thus protected by a coat that 



