AND DESERTS 131 



Europe meant the absence of such reservoirs of disease, 

 and accounts for the greater ease with which domesti- 

 cated ungulates were introduced there. It has been 

 suggested as a reason for the disappearance of so many 

 ungulates from South America — ^for they were once 

 abimdant there — ^that they were killed ofE by some 

 parasitic disease. If this were so, then with the dis- 

 appearance of the hosts the parasites must have died 

 also, leaving the field clear for reintroductions later. 

 In Africa we have to notice that the tolerance of minute 

 blood parasites — a tolerance doubtless originally ac- 

 quired at the price of a fearful death-rate — is a means 

 of protection of the existing forms against the intru- 

 sion of new and competing forms. The resistance to 

 the trypanosomes carried by the tsetse-fly has even to 

 some extent protected the antelopes from their great 

 enemy man, for European hunters are constrained to 

 avoid regions much infested by the tsetse on account 

 of the difficulties of transport. 



Another very beautiful ungulate which frequents all 

 the open parts of Africa south of the Sahara is the 

 giraffe, which shows a peculiar adaptation to Hfe in the 

 savana. The great elongation of the neck and of the 

 foreHmbs enables it to browse upon the leaves of 

 the acacias and other trees of the scrub. Despite the 

 length of the neck, however, drinking presents great 

 difficulties, the animal being compelled to straddle its 

 legs apart before it can reach to the ground. Grazing 

 is similarly difficult, and is rarely practised. The giraffe 

 inhabits arid coimtry, notably the Kalahari desert, and, 

 generally, sandy plains where the scrub on which it 

 feeds occurs. It can apparently go many months 

 without drinking. The animals go about in herds, and 

 are capable of great speed. Only a single young one is 



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