374 THE STRUCTURE AND LIFE OF BIRDS cuar., 
him the general direction in which he is to travel. 
This instinct is, no doubt, helped by the eyes, for in- 
stance in choosing the narrowest passage when a 
voyage over sea has to be made. Flying at a great 
height a Swift will be able on a clear night to see the 
striking features of the country from a long way off, 
and this will help him to keep his course. But the 
eye cannot do more than assist and correct the instinct. 
The migrant’s faculty differs from that of the Pigeon, 
in that it directs him to a place with which, not he, 
but his parents, are familiar. Marvellous as this no 
doubt is, we must be very careful not to exaggerate 
the miracle. The young Swallow has only to make 
for the south, not to find any exact spot. When he 
returns in spring, he often steers for the particular 
barn or chimney where his earliest days were passed, 
Moreover, though the young birds are the first to 
start, it is believed that there is much loitering on 
the autumn migration, and it is possible that they 
may be overtaken by the old birds and attach them- 
selves to them. Whatever may be the power by which 
they guide themselves, in many of them it is im- 
perfectly developed and fails them in their need. 
On no other supposition can we account for the fact 
that so small a percentage ever return. 
Though we decide that they find their way by in- 
stinct, we have not advanced far towards the under- 
standing of the problem. An instinct is an inborn 
faculty, distinct from reason, though reason may act 
upon it and modify it, and this ‘particular instinct we 
cannot understand, because we have something only 
very remotely similar to it in ourselves. In attempt- 
