36 EVOLUTION AND DISEASE. 



what looks like, in so far as shape and size are con- 

 cerned, an admirable pair of wings. A dissection of 

 the pectoral muscles is suggestive, for they are thin, 

 flat, and contain but little contractile tissue. The 

 prominent keel so conspicuous on the sternum of fly- 

 ing birds is, in Stringops, a mere ridge. The intrinsic 

 muscles of the wings are pale, thin, and composed 

 largely of fibrous tissue (fig. 17). 



It has been inferred that these birds have not long 

 been inhabitants of New Zealand only, but were de- 



FIG. 17. The Owl-parrot, or Kakapoe (Stringops habroptilus). 



veloped in other countries where their wings were of 

 use to them. The disuse of the wings is due to altera- 

 tion in environment. 



The atrophied wing muscles in the owl-parrot recall 

 the observations of Rengger who attributes the thin legs 

 and thick arms of the Payaguas Indians to successive 

 generations having passed nearly the whole of their lives 

 in canoes with their lower extremities motionless. 



Atrophy of parts useful for a brief period. Very 

 many organs are useful for a brief period, and later 



