CHAPTER XXII. 



PRELIMINARY NOTES ON THE DEVELOPMENT OF THE WING 



That the different sections of the wings of the hoatzin 

 and the common fowl change appreciably in proportion dur- 

 ing the growth of the birds has been demonstrated by Pycraf t 

 and others. These writers show that the changes taking place 

 in each are more or less parallel. 



The forearm of the newly hatched hoatzin is much short- 

 er than the hand, though in the adult it is longer. In the 

 embryo of about two-thirds development both are practically 

 of the same length, the hand being a trifle shorter. The 

 forearm, though now slightly larger, soon after hatching 

 shortens to the same length as the arm, which it parallels 

 until maturity. A glance at the following figures will show 

 that the development of each is in a directly opposite 

 direction : 



Opistliocomus hoazin (Illiger) 



Arm Forearm Hand 



Embryo (% dev.) 73.6 mm. 69.6 mm. 68.2 mm. 



2 day nestling 69. " 66.25 " 79.65 " 



10 " 63.6 " 63.6 " 82.6 " 



14 " 74.7 " 74.6 " 80. 



Juvenile 72. " 73. " 66.5 " 



Adult 71. " 80. " 65. 



Note: All the dimensions in the above and preceding figures were ob- 

 tained by using the adult measurements as a constant. The measurements of 

 the young birds were increased so that if the birds were actually as large as the 

 adult the length of their arm segments would be as in the above columns. 



The development of the wings of the jacana and the 

 ani are discussed in other chapters where the great amount 

 of variation in both is shown. There is a similarity between 

 the two; both show the lengthening of the immature hand 



