DEVELOPMENT OF WING 



343 



FIG. 111. DIAGRAM OF WING DEVELOPMENT OF THE HOATZIN 



and its decrease at maturity. The great possible varial)ility 

 of the arm first becomes apparent in the jacana, the growth 

 of that segment being quite the opposite of that of the hand, 

 while the middle section remains practically constant 

 throughout all stages. 



Though the different portions of the wing are nearly 

 equal in the adult blue-wdnged parrakeet, there is a consid- 

 erable variation in the earlier stages of growth. 



Psittac u hi passerin a ( Linn. ) 



Arm Forearm Hand 



24 hour nestling 26.2 mm. 20.7 mm. 24.4 mm. 



3 day " 24.6 " 19. " 18.4 " 



7 "* " 23. " 22.4 " 17. 



Adult 21. " 20.5 " 21.5 " 



Both the arm and the hand of the twenty-four-hour 

 nestling are longer than in the adult, while the forearm is 

 about the same. The arm decreases steadily to maturity 

 through all stages. The whole wing, however, at three days, 

 is shorter than in the adult, the hand in particular having 

 greatly decreased until slightly smaller than the forearm and 

 considerably shorter than the mature hand. By the seventh 

 day it is still comparatively shorter, w^hile the forearm has 



