I 



ANIMALS— PHYSICAL ENVIRONMENT 101 



spring and early summer. One obtains such crea- 

 tures as woodlice ; millipedes and centipedes ; 

 spiders, scorpions, mites and pseudo-scorpions ; 

 lepismids, Japyx, earwigs, cockroaches, crickets, 

 very numerous beetles, bugs, ants ; snails and 

 occasionally slugs, and earthworms. What befalls 

 these animals in the hot and dry season is largely 

 a matter of conjecture. Probably some descend 

 deep into cracks in the soil, and others aestivate 

 in the egg and possibly in other stages. Spencer 

 attributed the existence of land-snails in Central 

 AustraUa to various factors in different species. 

 Some existed on the shady side of hills, others 

 sestivated among tree roots, others closed the mouth 

 of the shell with a plug of mud ; others again were 

 minute and descended deeply into the clefts in 

 the soil. It is at any rate certain that the rich 

 fauna that one finds under stones in Persia, Pales- 

 tine, Algeria, and other stony deserts, in spring- 

 time is almost as ephemeral as the annual flowers, 

 and it is very remarkable that such moisture- 

 loving forms as snails and earthworms should be 

 able to exist through the summer in any stage in 

 these countries. 



The geographical distribution within the Great 

 Palaearctic Desert of these multitudes of smaU 

 creatures depends among other factors on the 

 presence of stones under which to shelter, and of 

 regularly recurring rainfall, but a very similar associa- 

 tion may be found in Lower Mesopotamia, a stoneless 

 plain consisting of nothing but the finest silt carried 

 down by the Tigris and Euphrates ; in this country 



