Natural History 465 



Two or three blind and naked young ones are born in a large 

 nest of moss and leaves and twigs, which the monogamous par- 

 ents build among the branches. There is strong maternal care 

 and courage, and when danger presses the mother may carry 

 one baby after another in her mouth to some place of safety. 

 There is considerable instruction in athletics and woodcraft. 



When winter comes the Squirrel does not hibernate, though 

 on a very cold morning it may sleep late within the hollow tree. 

 It still finds seeds and shoots to eat, and when these are scanty 

 it searches about for the caches of nuts it made in September 

 and October and forgot all about! Too much has been made 

 of the Squirrel's thrift. 



7 

 The Aerial Mammals 



Although the scanty fossil remains of Bats have revealed 

 nothing as to their ancestry, it seems safe to say that they 

 evolved from an Insectivore stock. Specialised as they are for 

 flight, they show numerous affinities with tree-shrews and the 

 like. The vacillating rapid flight is familiar, and in some bats the 

 power of flight is enough to enable them to migrate as birds do. 



In relation to the bat's twilight habits, the sense of touch 

 is highly developed on the wing, and about the nose and ears, 

 so that obstacles like branches are avoided. Perhaps there is 

 a pressure-sense distinct from touch, for bats often swerve to 

 one side before they are near the obstacle. It has been suggested 

 that the bat's cry of short-length sound-waves has a sort of 

 echo from surfaces, and that this warns the bat from collision. 

 There is, usually, only one young one at a time, an important 

 restriction for a flying mother that has to carry the offspring 

 about with her after birth as well as before. The back teeth of 

 small bats bear sharp cusps, well suited for crunching insects, 

 and a crowning adaptation may be found in the winter sleep of 

 the bats of northern countries. 



