142 THE NATURAL HISTORY OF SELBORNE. 
withdraw with us the latest of any species. Unless these 
birds are very short-lived indeed, or unless they do not return 
to the districts where they are bred, they must undergo vast 
devastations somehow, and somewhere; for the birds that 
return yearly bear no manner of proportion to the birds that 
retire. 
House-martins are distinguished from their congeners by 
having their legs covered with soft downy feathers down to 
their toes. They are no songsters; but twitter in a pretty 
inward soft manner in their nests. During the time of breed- 
ing they are often greatly molested with fleas.’ 
LETTER XVII. 
RINGMER, near LEWES, Dec. oth, 1773. 
I received your last favor just as I was setting out for this 
place; and am pleased to find that my monography met with 
your approbation. My remarks are the result of many years’ 
observation; and are, I trust, true in the whole ; though I do 
not pretend to say that they are perfectly void of mistake, or 
that a more nice observer might not make many additions, 
since subjects of this kind are inexhaustible. 
If you think my letter worthy the notice of your respectable. 
society, you are at liberty to lay it before them ; and they will 
consider it, I hope, as it was intended, as a humble attempt to 
promote a more minute inquiry into natural history; into the 
life and conversation of animals. Perhaps, hereafter, I may be 
induced to take the house-swallow under consideration ; and 
from that proceed to the rest of the British Azrundines. 
1 Reference is made to the parasites of swallows in the previous letter ; 
further allusions to the same subject are made in Letters XX and XXI. 
