IX. 



RETROGRESSIVE DEVELOPMENT 

 IN NATURE. 



Evolution in the animal and vegetable kingdoms is generally 

 understood to mean an uninterrupted progress from lower to 

 higher forms of life. Such a view is not, however, strictly 

 correct ; for retrogression plays an important part in evo- 

 lution, as is shown by the fact that an investigation into the 

 history of degenerate forms often teaches us more of the causes 

 of change in organic nature than can be learnt by the study 

 of progressive ones. Such investigation is, therefore, of the 

 deepest interest. 



To begin with a well-known instance, we are all aware of 

 the existence of birds which cannot fly, and of some among 

 them which do not even possess wings. One of these is the 

 Apteryx of New Zealand, called by the natives ' Kiwi-kiwi.' 

 The most superficial observer would at once remark that this 

 bird lacks something, since it reminds one of a man without 

 arms ; for the wings are totally absent, and the place where 

 they should be, is covered with a close smooth growth of hair- 

 like feathers. 



Not very long ago the question why this bird should lack 

 wings would have been regarded as sufficiently answered by 

 reference to its mode of life. The Kiwi lives in woods, not in 

 the trees, but on the ground ; in the day-time it hides in holes 

 in the ground, and comes out warily at night to hunt the worms 

 and insects which form its prey. It has no need of wings to 

 obtain its food, nor does it stand in any fear of native enemies 

 on the ground ; for two species of bat are the only representa- 



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