BILLS OF SKIMMING BIRDS. 231 



feathers of their breast, and then remove with the 

 bill. All the petrels have the nostrils enclosed in 

 separate tubes — sometimes single, and sometimes 

 double ; but the use of these in their economy is not 

 knovra. 



With the storm-petrels one group of sea-birds, 

 classed according to their habits in feeding, and the 

 structure of their feeding organ, may be said to ter- 

 minate ; but there is still another, the commencement 

 of vrhich may again be taken from the shore, and 

 traced to the more extended pastures of the other. 



The group w^hich has now been mentioned as ex- 

 tending from the gannet to the storm-petrel inclusive, 

 may be regarded as having a relation (such a loose 

 relation of mere analogy as can exist between preyers 

 at sea and preyers on land) to the birds of prey — the 

 gannets and races which have similar habits to the 

 eagles, the petrels to the vultures, and the storm- 

 petrels to the birds which catch insects on the wing. 

 The analogy is, as has been said, a loose one ; but it is 

 of use in forming a relative estimate of the economy 

 of the sea and Ihe land. 



We may. therefore, continue it with the remaining 

 sea-birds, which are principally the lestri or skuas, 

 the gulls, and the terns. These are the omnivorous 

 birds of the ocean ; but the term, as ^applicable to 

 that element, does not include vegetable food, though 

 many of these sea-birds feed on land during the 

 breeding season, and also when the sea becomes too 

 stormy for them. 



The leshi, though called eagles (the real sea-eagles 

 are land-birds), are the ravens of the deep ; and in 

 their bills, their claws, and the general cast of their 

 bodies, they have a raven-like air. The following is 



