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CXXXVI1 
preventing these butterflies and moths from crossing over and 
becoming established on the southern side of the Mediter- 
ranean. As most of the absentees are species which extended 
their range after the glacial epoch from east to west, it is 
understandable that those forms which are rare in Spain have 
not reached Africa, but why species like our tortoiseshell, 
common in South Spain, should fight shy of Africa, while 
V. polychloros is abundant, must have a subtle reason as yet 
unknown to us. The Oleander Hawkmoth is even a more 
instructive illustration of this phenomenon of distribution 
which appears anomalous to us. This beautiful moth is very 
plentiful in the Ethiopian Region, inclusive of the Malagassic 
Province, as well as in Asia Minor, Western Central Asia and 
Western India southward to Ceylon; it has extended its 
range westward in the countries north of the Mediterranean 
and is an occasional visitor in Central and West Europe and 
Great Britain. In North Africa and Spain and Portugal 
where the food-plant is as abundant along the brooks and 
rivers as the willow is in northern Europe, the moth is as 
rare a visitor as in Germany or England; besides a few larvae 
found at El Kantara, Bone and Alger, I have no evidence 
that the species occurs in Algeria, although every collector 
searches for it on the oleander bushes. The country is 
accessible to our species, there is an abundance of food not 
eaten to any extent by other insects and left alone by mammals, 
and the climate appears at least as suitable for this tropical 
hawkmoth as the South of France, where the species is a 
permanency; why does the species not likewise establish 
itself in Algeria? The reason remains as yet obscure. 
Another interesting absentee from the countries south of 
the Mediterranean is the genus Parnassius, which is repre- 
sented in Italy and Sicily by two species and in Spain by one 
and might be expected to occur in Morocco and Eastern Algeria. 
I do not believe that the genus has reached North Africa, for 
the following reasons. The Parnassius apollo of the Sierra 
Nevada is evidently excessively rare, and may even have 
become extinct in recent years, which we may interpret as 
evidence that this southern locality was not very favourable 
for the insect. If that is so, an even more southern mountain 
