:}.)(; 



TROPICAL WILD LIFE IN BRITISH GUIANA 



FIG. 120. DIAGRAM OP" HAND DEVELOPMENT OF THE BLACK-NECKED TOUCAN 



goiii^' oil, as the flight of the hirds gradually changes. Their 

 flight in general is of a})oiit the same strength, and naturally 

 it follows that they should develop along more or less paral- 

 lel lines. There are exceptions to this — as will be shown — 

 in which the power of flight has been either increased or de- 

 creased and a change in the development of the hand shows 

 accordingly. 



In such birds as the toucan, the ani, and the catbird, 

 which do not greatly use their wings in their daily round of 

 life, there is little or no variation in the growth of either of 

 the hand segments. Though the actual proportion of the 

 car])us to the digitus may vary somewhat in the different 

 bii-ds, due possibly to different ancestral or even present day 

 habits, the actual method of growth remains practically the 

 same. 



Ptcroglos.siis aracari (Linn.) 



Carpus Digitus 



() day nestling 21.3 mm. 13.5 mm, 



•21 "* " 21.5 " 13.5 " 



iVdult 22. " 13. 



Galcoscopfcs caroliiicnsis {Iawu.) 



Carpus Digitus 



Kmbryo 13.8 mm. 9.2 mm. 



3 day nestling 12.5 " 10.5 '' 



f) "* '^ 13. " 10. 



Adult 13.5 " 9.5 " 



