35() TROPICAL WILD LIFE IN BRITISH GUIANA 



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



goini>' on, as the flight of the hirds "Tadiially clianges. Their 

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

 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 difl^erent 

 birds, due ])ossil)ly to difl'erent ancestral or even present day 

 habits, the actual method of growth remains practically the 

 same. 



Ptcroglos.sKS aracari (Linn.) 



Carpus Digitus 



6 day nestling 21.3 mm. 1.3.5 mm. 



21 "' " 21.5 " 13.5 " 



Adult 22. " 13. 



Galeoscoptcs caroUnensis (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 " 



