246 GKALL^E. 



bounds than those of the white-throat. The same argument 

 applies to the crakes, and indeed to all migatory birds that 

 find their food upon the land, or along the margins or in the 

 shallows of the inland waters. 



With sea-birds it is different, though even among them, 

 and more especially among the wading species of them, the 

 law can still be traced, though far more faintly. That, how- 

 ever, is easily explained ; the more uniform temperature of 

 the sea renders the productions of its shores more uniform ; 

 and those currents of the sea which are produced by the 

 tides, distribute the products of the equatorial, and more 

 productive parts, to the very confines of the polar sea. The 

 currents, put in motion by the joint action of the trade 

 wind and westward wave of tide in the equatorial parts of 

 the Atlantic, strew the whole shores of the north with the 

 produce of that ocean ; so that food which is grown in the 

 West Indian seas may be laid down upon the shores of New- 

 foundland, Iceland, or even Spitzbergen, to feed the littoral 

 birds in the summer season ; nay, even the food of the whales 

 themselves, in the " green water," along the margin and in 

 the openings of the polar ice, is no doubt, in great part, the 

 production of more southern parts of the Atlantic. 



These remarks may, to systematists, appear to be inter- 

 polated somewhat out of place ; but the interpolation (which 

 is of course meant for the student, not for the master) is 

 intentional. Placing them here, after we have noticed the 

 habits of these birds, to which they apply, and from the 

 study of which they naturally and almost necessarily arise, 

 gives them the persuasive form of instruction, and not the 

 apparently arrogant one of assumed hypothesis : and though 

 there may be more glory to the author in bringing forward 

 general principles in large and imposing masses, there is 

 more use to the common reader in breaking them down 

 into manageable pieces, if the points of connexion are so 



