STEPPES AND DESERTS. 15 



torpid from cold, so here the crocodile and the boa-con- 

 strictor lie wrapt in unbroken sleep, deeply buried in the 

 dried soil. Everywhere the drought announces death, yet 

 everywhere the thirsting wanderer is deluded by the phan- 

 tom of a moving, undulating, watery surface, created by 

 the deceptive play of the reflected rays of light (the mirage, 

 36). A narrow stratum separates the ground from the 

 distant palm-trees, which seem to hover aloft, owing to the 

 contact of currents of air having different degrees of heat and 

 therefore of density-- 4 . Shrouded in dark clouds of dust, and 

 tortured by hunger and burning thirst, oxen and horses scour 

 the plain, the one bellowing dismally, the other with out- 

 stretched necks snuffing the wind, in the endeavour to detect, 

 by the moisture in the air, the vicinity of some pool of water 

 not yet wholly evaporated. 



The mule, more cautious and cunning, adopts another me- 

 thod of allaying his thirst. There is a globular and articulated 

 plant, the Melocactus (37), which encloses under its prickly in- 

 tegument an aqueous pulp. After carefully striking away the 

 prickles with his forefeet, the mule cautiously ventures to 

 apply his lips to imbibe the cooling thistle juice. But the 

 draught from this living vegetable spring is not always un- 

 attended by danger, and these animals are often observed to 

 have been lamed by the puncture of the cactus thorn. 



Even if the burning heat of day be succeeded by the cool 

 freshness of the night, here always of equal length, the wearied 

 ox and horse enjoy no repose. Huge bats now attack the 

 animals during sleep, and vampyre-like suck their blood ;f 

 or, fastening on their backs, raise festering wounds, in which 

 mosquitoes, hippobosces, and a host of other stinging insects, 

 burrow and nestle. Such is the miserable existence of these 



* This effect is well represented in Grindlay's Scenery of the Western 

 Side of India, plate 18. — Ed. 



t Modern naturalists affirm that all bats are insectivorous. — Ed. 



