236 MOSTLY MAMMALS 
itself, expanding the membrane which joins the feet to the 
body, like a parachute. The skin is used as an ornament. 
I think it is identical with one very common in the island 
of Ceylon, which is almost tame.” 
The extraordinary misconception as to the affinities of 
the creature displayed in the last sentence of this quotation 
will be apparent when I say that the scale-tailed squirrels 
—whether furnished with a flying membrane or not—are 
absolutely restricted to Africa, where not a single repre- 
sentative of the true flying-squirrels of Asia and Europe 
exists. 
The reason why these two very dissimilar groups of 
animals are regarded in popular estimation as near relatives 
is, of course, due to the fact that both are furnished with 
expansions of skin by means of which they are enabled 
to take flying leaps from bough to bough. Such flying 
membranes are developed in very few mammals, and the 
popular idea is that the presence of such a membrane must 
necessarily imply intimate affinity between all the forms in 
which it occurs. Hence not only are the African flying 
scale-tailed squirrels associated with the typical flying- 
squirrels, but the still more widely separated flying-phalangers 
of Australasia are likewise regarded as members of the same 
group. 
In making such associations the public fail to recognise 
that similar structures may be produced in totally different 
groups of animals owing to their living under similar special 
conditions, or having peculiar habits of the same nature. In 
external appearance rodents belonging to different families, 
such as squirrels and dormice, may be very much alike; 
and if certain members of each group had acquired the same 
mode of life as the flying-squirrels, their similarity would 
probably have become still more noticeable. For unless 
