344 TROPICAL WILD LIFE IN BRITISH GUIANA 



FIG. 115. DIAGRAM OF WING DEVELOPMENT OF THE TRUMPETER 



lengthened until it is larger than in the adult. Thus in seven 

 days the conditions of the hand and forearm directly alter- 

 nate. They return to their former state at maturity, though 

 the hand is not proportionally quite so large as it was in the 

 newly hatched chick. 



The longer wing of the twenty-four-hour nestling is 

 probably a reminder of bygone ages, when the wing was 

 longer at maturity than at present. The excess of length, 

 it is evident, was chiefly in the upper arm, upon which some 

 change of condition has acted, causing a gradual reduction 

 without materially affecting the other portions of the wing. 



Psophia crepitans (Linn.) 



Arm Forearm Hand 



6 day chick 74.2 mm. 58.5 mm. 75.9 mm. 



14 " " 74.4 " 67.4 " 73.6 " 



Adult 77. " 73. " 65. 



There is a decrease of the hand in the grey-backed trum- 

 peter (Psophia crepitans) as compared with an increase of 

 the forearm. The arm also gradually increases, but to no 

 such extent as the next section. Some of the shortening of the 

 hand is doubtless due, as in the hoatzin, to the reduction of 

 the claws, for in the young bird there are the remnants of 

 two, one on the thumb and one at the tip of the wing. The 



