356 



TROPICAL WILD LIFE IN BRITISH GUIANA 



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



going on, as the flight of the birds gradually changes. Their 

 flight in general is of about 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 

 carpus to the digitus may vary somewhat in the different 

 birds, due possibly to different ancestral or even present day 

 habits, the actual method of growth remains practically the 

 same. 



Ptcroglossus aracari (Linn.) 

 Carpus 



6 day nestling 21.3 mm. 



21 " 21.5 " 



Adult .. 22. 



Digitus 

 13.5 mm. 

 13.5 " 

 13. 



Galeoscoptes carolinensis (Linn.) 



Carpus Digitus 



Embryo 13.8 mm. 9.2 mm. 



3 day nestling 12.5 " 10.5 " 



6 " 13. " 10. 



Adult ... 13.5 " 9.5 " 



