NOTES ON EMBRYOS 325 



with down sheaths, instead of being flattened with the pro- 

 tuberance reduced. There is no trace of feathers about them 

 in the adult. (Fig. 111.) 



The feathering of the tarsus is much heavier than in the 

 adult, this area, in the embryo, being one of the most heav- 

 ily feathered portions of the body. The scutation of the hind 

 tarsus is very sharply defined, the scutes being clear cut and 

 overlapping one another like fish scales. 



The wing has a claw on the thumb and one at the tip. 

 Both claws are long and well developed. In this character 

 the embryo differs entirely from the adult which, so far as 

 I have been able to determine, is entirely without claws. 



II 



Guiana Kiskadee Pitangns sulphuratus sulphuratus (Linn.) 



PTERYLOSIS 



The first signs of any pigmentation of the feather pa- 

 pillae in the embryonic stages may be found when the em- 

 bryo is about three-fifths developed. The longest papillae 

 belong to the dorsal tract, though only the posterior portion 

 of this shows. Commencing in the pre-sacral region it imme- 

 diately divides into two single rows of sheaths which follow 

 the line of the ilia and come together in the post-sacral 

 region near the naked eurypygium. These sheaths are also 

 the longest on the freshly hatched bird and reach a length 

 of 15 mm., while the remainder of the tract is represented 

 only by undeveloped papillae. The sacral space is narrowed 

 down to a narrow cleft. 



What at first appear to be rectrices in the earlier embryo 

 are really the highly pigmented upper coverts. The rectrices 

 are present only as mere shadows of papillae. In the hatch- 

 ing bird the upper coverts are very long while the rectrice 

 sheaths are just beginning to peep forth. As the bird grows 

 older, however, the rectrices grow rapidly and soon overtake 

 their coverts. 



