350 TROPICAL WILD LIFE IN BRITLSH GUIANA 



111 the half-fledged iiesthng of tlie Guiana spinetail 

 {SijnalUhvis (juiancn.sis) , the hand is (juite appreciably long- 

 er than in the adult, while the other sections follow the same 

 course as in the two preceding birds. 



Among other birds of the same order there is another 

 method of development in the wing, the difl^erence being that 

 the forearm lengthens and decreases instead of the hand as 

 previously mentioned. In the half-grown fledgling of botli 

 the kiskadee {Pitaiigus sulplmratus) and the silver-beaked 

 tanager {Bamphocchis carho) the forearm is decidedly larg- 

 er than in the adult. 



Pitangus sulphuratus (Linn.) 



Arm Forearm Hand 



Xewly hatched 30.1 nmi. 33.4 mm. 27.8 mm. 



14 day nestling 28.4 " 36.2 " 26.6 " 



Adult' 29. " 33.5 " 29. 



Here again is a case where a sudden increase of one 

 segment is accompanied by the decrease of another, though 

 this time there is diminution of both the hand and arm. 

 The total decrease of the two, however, equals the amount 

 of extra length in the forearm. 



The wing development of the grey-breasted martin 

 {Progne chahjhea) is slightly different from either of the 

 two preceding methods of growth. This is due to its ad- 

 vanced powers of flight, which necessitates a rather length- 

 ened hand, though both the forearm and hand are propor- 

 tionally smaller in the younger stages than in the adidt. 



Progne cJial/jhca (Gmel.) 



Arm iForearm Hand 



3 day nestling 26. ,5 mm. 29.1 mm. 2.5.4 mm. 



7 "* " 24.1 " 27.7 " 29.2 " 



14 " " 20.9 " 28.4 " 31.9 " 



Fully fledged 19.2 " 30..5 " 31. " 



Adiiit 20. " 29. " 32. 



