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 
abundant there—that they were killed off 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 life in the 
savana. The great elongation of the neck and of the 
forelimbs 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 country, 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 
ber 
