88 NATURAL HISTORY 
from organic impulse, and not from the resistance 
of the air against the hollow of its mouth and 
throat. ; 
If ever I saw anything like actual migration, it 
was last Michaelmas day. I was travelling, and 
out early in the morning: at first there was a vast 
fog, but, by the time that I was got seven or eight 
miles from home towards the coast, the sun broke 
out into a delicate warm day. We were then on 
a large heath or common, and I could discern, as 
the mist began to break away, great numbers of 
swallows (hirundines rustice) clustering on the 
stunted shrubs and bushes, as if they had roosted 
there all night. As soon as the air became clear 
and pleasant, they were all on the wing at once, 
and, by a placid and easy flight, proceeded on south- 
ward towards the sea: after this I did not see any 
more flocks, only now and then a straggler. 
I cannot agree with those persons that assert 
that the swallow kind disappear some and some, 
gradually as they come, for the bulk of them seem 
to withdraw ‘at once ; only some stragglers stay be- 
hind a long while, and do never, there is the great- 
est reason to believe, leave this island. Swallows 
seem to lay themselves up, and to come forth in a 
warm day, as bats do continually of a warm even- 
ing, after they have disappeared for weeks. Fora 
very respectable gentleman assured me that, as he 
was walking with some friends under Merton wall, 
on a remarkably hot noon, either in the last week 
in December or the first week in January, he es- 
pied three or four swallows huddled together on the 
moulding of one of the windows of that College. 
I have frequently remarked that swallows are seen 
