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 Strzngops, 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- 
Fic. 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 
Reider tee: --: 
