FLIGHTLESS BIRDS AND THEIR FATE. 69 



the place of air, like ourselves, we see that this 

 cannot be the true explanation. 



Sometimes the whole body is thoroughly per- 

 meated with air. It runs in little bags between 

 the muscles of the body, and between the skin 

 and the body to a most extraordinary degree. 

 The common gannet of our shores, the pelican, 

 and the South American " screamer " are good 

 examples of this. 



CHAPTER V. 



FLIGHTLESS BIRDS AND THEIR FATE. 



To appreciate fully the significance of the fact 

 that there are birds to whom the power of flight 

 is impossible, that have never known what it is 

 to soar above the clouds, but who have been 

 confined, as were their ancestors, for countless 

 generations to Mother Earth, we must imagine a 

 race of men, or a family of men, who have never 

 walked. Yet there are such birds, and it is of 

 them that we are going to speak now. 



We have seen in the previous chapters how 

 different organs, or parts of the body, change 

 their shape, taking on new forms to adapt them- 

 selves, as the need arises, to new surroundings 

 or new food. In all these cases the result of this 

 adaptation has been an increase in the com- 

 plexity of the organ. 



With every part of the body in the same way, 

 so long as each particular organ continues to be 

 useful, so long as the organism has need of it. 



