THE MASTERY OF THE AIR 251 



Hawaii seem to think nothing of setting out for 

 Alaska ; it means some sense of direction that 

 we do not understand, for a young bird that has 

 never been more than a few miles from home 

 will start gaily in the autumn for tropical Africa 

 and will reach its goal in safety, and, what is 

 more, will sometimes come back again the 

 following spring to the precise place of its 

 birth. 



THE FOURTH SOLUTION OF FLIGHT 



The fourth solution of the problem of flight 

 was discovered by bats. In its idea it is nearest 

 that of the Flying Dragons, but it is quite in- 

 dependent and by itself. Bats are, of course, 

 true mammals, covered with hair, and giving 

 milk to their offspring. They are most nearly 

 related to the Insectivores, such as shrew and 

 mole, and it is interesting to notice that there is 

 in the Far East an aberrant insectivore called 

 Galeopithecus, placed by some authorities in 

 a special order, which has a sheet of skin 

 stretched between fore- and hind-limbs, and 

 is a very expert parachutist. 



The wing of the bat is formed of a fold of 

 skin, which usually begins at the shoulder and 



