306 DEFICIENCIES IN OUR LIST. 
which with us are scarce,—the Redstart, Grasshop- 
per Warbler, Lesser Whitethroat, and Pettychaps. 
The Nightingale is common in Oxfordshire but in 
Devon has not been noticed far west, though in 
Dorset it is plentiful, hereby defining very accu- 
rately its south-western limits in England. Now 
in all these instances of remarkable dissimilarity 
between the two counties, no explanation what- 
ever can be given of the preference for localities 
so observed. The distribution of some animals is 
latitudinal, that of others longitudinal, some species 
inhabit a district of a rounded or irregular form, 
some are found regularly dispersed through the 
whole of a natural geographical division of the 
globe, some are found inhabiting one division and 
only partly one or more of the others, some inhabit 
one or more countries, omitting or refusing to dwell 
in certain spots in that range, whether large or 
small, some are uncertain in their stations, are 
continually changing their position, or remain an 
indefinite period and then disappear in toto, or 
return after the lapse of some time; in all which 
phenomena little can be detected of secondary 
causes exercising a decided influence, and yet I 
cannot but think we are largely indebted to these 
causes for the great variety of natural productions 
of which we boast, allowing all necessary weight 
to those unknown primary laws of dispersion under 
which very many species appear with us, and many 
are denied to us. But depending upon all these 
causes combined, we are enabled to rank as Devon 
birds a very large number of rarities, perhaps more 
than any other county in Great Britain. Perhaps 
the whole number of British birds may be considered 
as 302, and upon inquiry where our deficiencies of 
53 chiefly occur, it is found that they consist in 
part of stragglers and rarities, and in part of birds 
whose limits of distribution are confined to the 
