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CXXXVill 
where they catch, shoot and eat them. There obviously is 
inherent in this species a strong aversion to crossing the water, 
the explanation probably being that in postglacial times this 
southern bird found its biological boundary at the northern 
shores and now shies at a barrier which resembles in appear- 
ance, but not in fact, the original boundary of its range. 
The behaviour of migratory birds is a case of a similar kind. 
In Algeria we find large numbers of species which are winter 
visitors or pass through the country. Many of them are 
represented in Mauretania by resident local races, which are 
often so shghtly different that only the experts can distinguish 
them, and it is quite natural to conclude—and formerly this 
was the general opinion—that many individuals born in 
northern countries remain in North Africa, where all factors 
are quite favourable for them. But the fact is they do not 
stay, apart from occasional specimens unfit for one reason or 
the other to undertake the flight across the Mediterranean. 
Why do they all go back to the north? The life of these 
migrants like that of the crested lark is governed by instinct, 
or to use a more lucid term, by inherited memory, one of the 
greatest forces in the life of animals inclusive of man. Bernard 
Shaw is quite right in saying that the opinions and actions of 
the average man are to a large extent based on the raw feelings 
emanating from our subconscious selves unchecked by con- 
sidered judgment, and that applies as well to the actions of 
animals. The distribution of animals does not entirely depend 
on outward causes, but there are also psychological factors 
which must be taken into account. 
When I use to-night the term Algeria, I do not wish to 
imply that this political term designates faunistically a unit 
separate from Tunisia and Morocco, or that the country is 
homogeneous in itself. Algeria as a whole differs much less 
from Tunisia and Morocco in fauna and flora than do the 
physiographically different districts of Algeria from one 
another. The tourist who visits Algeria in winter in search 
of sunshine and travels by rail or motor from the coast across 
the country to Biskra in the northern desert, traverses the 
three zones into which the country is faunistically and botanic- 
ally divided in conformity with its physiography. These 
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