76 ASPECTS OF TROPICAL NATURE 



distance they approach as cautiously as possible ; and when 

 about a mile distant, they unleash their greyhounds, who dart 

 off with the rapidity of arrows, and are excited, by loud cries, 

 to their utmost speed. Yet they only reach the flying herd 

 after a long chase ; and now the scene acquires the interest of 

 a drama. The best greyhound selects the finest gazelle for his 

 prey, which uses all its cunning to avoid its pursuer, springing 

 to the right, to the left, now forwards, then backwards, some - 

 times even right over the greyhound's head ; but all these zig- 

 zag evolutions fail to save it from its indefatigable enemy. 

 When seized it utters a piteous scream, the signal of the grey- 

 hound's triumph, who kills it with one bite in the neck. 



Several lizards inhabit the desert; among others, a large 

 grey monitor, and a small white skink, with very short legs, 

 called Zelgague by the Arabs. Its movements are so rapid 

 that it seems to swim on the sand like a fish in the water,. 

 and when one fancies one has caught it, it suddenly dives 

 under the surface. Its traces, however, betray its retreat, and 

 it is easily extracted from its hole, — a trouble which, in spite of 

 the meagre booty, is not considered too great when provisions 

 are scarce. 



According to the seasons animal life fluctuates in the Sahara 

 from north to south. In winter and spring, when heavy rains, 

 falling on its northern borders, provide wide districts, tho- 

 roughly parched by the summer heat, with the water and 

 pasturage needed for the herds, the nomadic tribes wander 

 farther into the desert with their camels, horses, sheep, and 

 goats, and retreat again to the coast-lands as the sun gains 

 power. At this time of the year the wild animals — the lion, 

 the gazelle, and the antelope — also wander farther to the south, 

 which at that time provides them, each according to its taste, 

 with the nourishment which the dry summer is unable to be- 

 stow ; while the ostrich, who during the summer ranged farther 

 to the north, then retreats to the south ; for hot and sandy 

 plains are the paradise in which this singular bird delights to 

 roam. 



In the southern part of the Sahara the tropical rains, whose 

 limits extend to 19° N. lat., and in some parts still farther tq 

 thp north, produce similar periodical changes in the cliaracter 



