DEVELOPMENT OF WING 355 



backed cac'i(jiic', <^iaiit cacicjuc {O.sdiKfjj.s) , silver-beaked 

 tanaL',er and l)lue-wiiioed ])arrakeet, all with «»ood average 

 flights, but which have a small variation of the carpus and 

 digitus during their development. 



Piiducjus siilpliurafus (Tiinn.) 



Carpus Digitus 



% Embryo lO.oO mm. 13. 4 mm. 



Newly hatched nestling ... 16. " 13. 



14 day nestling 16..5 " 12.4 " 



Adult 17. " 12. " 



Birds that have remnants of claws are doubtless, as a 

 rule, the ones in which the fingers were functional most re- 

 cently. Traces of this character have not yet been lost; so 

 consequently the hands still function ontogenetically, to fit 

 the requirements of fingers, as in the hoatzin. In most cases 

 of altrical birds the loss of this character either antedated or 

 paralleled their helplessness; otherwise there would have 

 been little need foi- a change to the present state and we 

 would still see all tiny nestlings crawling about the branches 

 like little hoatzins. That this was true may be recognized 

 from the great variation of these parts in the embryo of 

 todaj^ 



The functional fingers being lost at this comparatively 

 early date, it was natural for the parts of the hand to adjust 

 themselves to the new conditions; and this adjusting is still 



FIG. 119. DIAGRAM OF HAND DEVELOPMENT OF THE GUIANA KISKADEE 



