824 



TROPICAL Wir.n T.IFl", IX BRITISH GUIANA 





FIG. 111. DEVELOPMENT OF BILL OF THE DUSKY NIGHTHAWK 

 a. Embryo. 6. Adult. 



EXTERNAL CHARACTERS 



The embryo has the general appearance of being tufted 

 and spotted with down sheatlis. The featliering of the head, 

 wings and feet, and the curious shape of the bill give it an 

 individuality of its own. Tlie auditory apertures are large, 

 pear-shaped and very close to the gape, the knob-like nos- 

 trils being placed rather near the tip of the upper mandible, 

 which, with its rounded "egg-tooth" and curved end, looks 

 very different from that of its parent. The bill is more com- 

 ])ressed than depressed and its frontal half is very narrow 

 with the gape extending below the center of the eye. The 

 lower mandible is enlarged at the tip, but tliere is no lower 

 "egg-tooth" as in pigeons. 



The nasal apertures are round and point directly out- 

 ward. They are placed in the lower portion of large, round- 

 ed, fleshy protuberances whicli arise on either side of the man- 

 dible. JNIidway between the nostril and the tip of the bill 

 is a patch of black pigment whicli is directly above a similar 

 spot on the lower mandi})le. The upper mandible also is 

 slightly pigmented along its cutting edge. 



From the above it may be gathered that the embryonic 

 bill varies much in external characters from the adult. It is 

 much narrower, much more compressed and the gaj^e is not 

 so deep. The nostrils are round, protrude, and are fringed 



