646 . WILSON'S PETREL. 



to I twelfth, and is rather less in the rectum, which is terminated by a 

 very small globular cloaca, J, 3i twelfths in diameter. There are no 

 cceca. The intestine measures 14 inches. The stomach properly so 

 called is lined by a rugous epithelium, and is in fact a true gizzard. It 

 contains a quantity of shell-sand. The inner surface of the proventri- 

 culus is soft and smooth ; that of the oesophagus longitudinally plicate. 

 The trachea is 1| inch long, from 1^ twelfth to 1 twelfth in breadth, 

 flattened, with rings 84 in number, slender, and unossified. Bronchi 

 wide, of 25 half rings. 



In the structure of the digestive organs this species closely agrees 

 with that of Thalassidroma pelagica, as will be seen by referring to Vol. 

 IV. p. 314 ; and the curious modifications which they present are among 

 the most interesting of the many that have been briefly described and 

 figured in these volumes. With this interesting bird terminates a se- 

 ries of anatomical details, which, imperfect as they are, however care- 

 fully they have been executed, it is hoped will form a basis for more 

 extended observations. They present a new and most important fea- 

 ture in the ornithology of North America, which in this respect at least 

 is not now much behind that of other countries. 



