240 MOSTLY MAMMALS 
But it may be taken as certain that the flying scale-tails— 
of which, by the way, there are two distinct generic types 
(Anomalurus and Idiurus)—are the specialised descendants 
of acreature closely allied to, if noc identical with, Zenkerella. 
It may further be affirmed with certainty that the evolution 
of the flying from the non-flying scale-tails has taken place 
in Africa. Whether, however, Zenkerella itself is an aborigi- 
nal African type, or an immigrant into the dark continent 
from the north, is a question difficult to answer at the 
present time. 
Although the flying-squirrels of Europe and Asia have 
been known from time immemorial, their pedigree is not 
so easy to trace as is that of the scale-tails. Probably 
they were evolved from non-flying squirrels at an earlier 
date than that at which Asomalurus branched off from 
Zenkerella (or its prototype), as they appear to be repre- 
sented by teeth in some of the earlier Tertiary deposits 
of Europe. It is therefore quite probable that even the 
generic types from which they trace their descent have 
died out. Nevertheless, it may be considered practically 
certain that they are descended from rodents more or less 
nearly allied to the true squirrels of the genus Sczurus. 
Their pedigree is therefore wholly distinct from that of their 
reputed cousins, the scale-tailed flying-squirrels of Equatorial 
Africa. 
In appearance the true flying-squirrels, of which there 
are three distinct generic types, are very similar to 
ordinary squirrels, as indeed they are in their habits; 
their long flying leaps, during which they half float in the 
air by the aid of the parachute, being only an extension 
of the bounds taken by the ordinary red squirrel in its 
passage from tree to tree. Many of them are even more 
beautifully coloured than ordinary squirrels. Compared 
