NOTES ON THE STRUCTURE OF BIRDS. 
OETALIDA RUFICAUDA, Jabdine. 
Many forms of the Craosiclce, with others allied to them, present 
remarkable conformations in the structure of the trachea. That of 
a duplicature upon the breast, just within the skin, occurs in several 
of them, as well as in some aquatic birds, some of the waders, and 
in a few incessorial birds. It is a structure of which we do not 
perceive the use or intention, and one which would apparently ex- 
pose a very important organ more readily to injury. Most of the 
species of Penelope and Ortalida possess a very loud and shrill 
voice, often harsh and discordant, and which at times they utter 
incessantly; some of the notes have a deep or internal sound, as 
if produced from within, and several have the power of modifying 
their tones, and of making them appear as if uttered at various 
distances ; a power however which is possessed even in a greater 
degree by many species that have no winding or analogous structure 
of the trachea. 
In the species before us, for which we are indebted to our Tobago 
correspondent Mr. Kirk, and which we have ventured elsewhere 
to characterize as undescribed, a comparison of the structure with 
that of the trachea of the Parraka described and represented by 
Dr. Latham, and with M. Temminck’s plate of the same organ, from 
his Penelope Parrakoua , presents some differences. In both these 
the trachea is seen with the sternal keel in the centre, the duplica- 
ture running down the one side and up the other. In the Parraka 
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