64 PASSERES. TROCHILID^E. 



breast-bone (sternum) of great surface in propor- 

 tion. Hence their flight is swift and vigorous, 

 perhaps in a degree greater than that of any other 

 birds ; and it is capable of being long, almost con- 

 stantly, sustained during day without fatigue. By 

 the inconceivably rapid vibration of these power- 

 ful wings, they have the power, possessed by many 

 insects, of poising themselves in the air, where 

 they hang apparently motionless, while their 

 wings, through the extreme swiftness of their 

 oscillations, are rendered invisible, except as an 

 undefined misty cloud on each side. The vibra- 

 tion of these organs produces, by their impact 

 upon the air, a humming or whirring sound, more 

 or less shrill according to the species, whence the 

 common name of the birds is derived. Their feet 

 are small and weak, and are in little request, so 

 much of their time being passed upon the wing. 



HEAD OP LAMPORNIS PORPHYRURUS. 



The beak is long and slender, sometimes straight, 

 sometimes curved downward, and in one or two 

 species even curved upward. The tongue is 

 slender and capable of protrusion to a great ex- 

 tent ; when recent, it presents the appearance of 

 two tubes laid side by side united for half the 

 length, but separate for the remainder. The 

 substance of these is transparent in the same 

 degree as a good quill, which, under a microscope, 

 they much resemble : each tube is formed by a 



