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settlement isolated from Europe by a wide stretch of desert. 
The influx of tourists is so great that the trains are usually 
crammed, and the hotels too small to accommodate the visitors. 
Even in winter, though the temperature in the Sahara 
is generally hot in daytime, the heat is not oppressive, the 
air being so very dry that one stands a high temperature 
much better than in the Tell. After a strenuous day one is 
pretty dried up and thirsty, and I agree with the writer who 
said that a great thirst is the most unpleasant sensation, 
and the quenching of it the most delicious. The best time 
for moths in the northern desert is May and June, but unfor- 
tunately that is also the time when the malaria begins to 
appear and renders a longer sojourn in any oasis rather danger- 
ous. It is advisable for an Entomologist to select a locality 
with firm ground such as Chegga, two stations below Biskra, 
where tufts and bushes of hardy perennials cover the ground, 
affording food for caterpillars even in very dry years. 
To the west of the sandy desert the ground gradually rises 
to form a kind of plateau of a considerable average height, 
where the wind has swept the sand away from the rocky 
ground into the depressions and where barren hills approach 
3000 ft. in height. This plateau, which does not descend to 
below 1200 ft., is traversed from north to south by the route 
Laghouat-Ghardaia. The territory is very different in appear- 
ance as well as flora and fauna from the eastern sandy desert 
with its monotonous salt flora, and here it is that many 
Palaearctic species have penetrated farthest south into the 
Sahara. The railway, fortunately, has not yet reached the 
desert in this western district, but, as it will be completed 
as far south as Laghouat in the near future, the country of 
the Mzab will be spoiled by the crowds of tourists as much as 
Biskra is to-day and Tougourt will be in a few years. I 
visited Ghardaia in 1911, collecting on the way in many places. 
The fauna of the Sahara as a whole is composed of three 
elements: genera and species derived from Tropical Africa, 
genera and species of Palaearctic origin, and genera and species 
of the desert belt. While the southern Sahara and its oases 
have an Ethiopian fauna, the northern districts of the Sahara 
are much more Palaearctic than Ethiopian. All classes of 
animals tell the same tale, the farther you go into the Sahara 
