CHAPTKR XXII. 



PREIJMINARY NOTES OX THE DEVELOPMENT OF THE WING 



Tluit the different sections of the wings of the lioatzin 

 and the common fowl change appreciably in proportion dur- 

 ino; the growth of the birds has been demonstrated by Pycraft 

 and others. These writers show^ that tlie 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. Tlie 

 forearm, though now slightly larger, soon after liatching 

 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 : 



Opisthocomus Jwazin (Illiger) 



Arm Forearm Hand 



Embryo (-3 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. " m.o " 



Adult 71. " 80. " 65. " 



Note: All the dimensions in tlie 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 segnnents woidd be as in the above columns. 



Tilt' (le\elopment of tlie wings of the jacana and the 

 aiii iu-e 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 



