IN THE SHETLANDS 183 
except perhaps sparrows—not counting poultry of 
course. Already the terns have gone a good deal 
further than the guillemots, for ‘they not only show 
the liveliest interest in the common progeny, and 
combine together for their defence, but there is also, 
I believe, a good deal of communistic feeding amongst 
them. Other birds, perhaps, have gone further still. 
In what does the interest taken by a bird—let us 
say by one of these guillemots—in a chick which is 
not its own originate? Does not the sight of it 
arouse, by association of ideas, all those feelings 
which, but shortly before, its own chick was daily 
arousing ? And if this be so, does it not in a manner 
mistake it for its own? It would be interesting, 
were something to happen to the parents of this 
little chick, to see if it would be fed and taken care 
of by any of the other birds on the ledge. If it were 
to be, I should be inclined to think this the reason of 
it. That one bird (or pair of birds) should foster the 
young of another, knowing all the while that it was 
another’s, and not its own, seems to me very unlikely. 
There must be some confusion of thought. By asso- 
ciation of ideas the stranger chick would excite in the 
stranger bird the feelings proper to rearing, whilst at 
the same time supplying in itself the proper object 
for their translation into act. When once this point 
had been reached, the foster-parent, if it did not look 
upon the chick as its own, would have—always sup- 
posing it to be one of these guillemots here—to 
retain a clear recollection of the chick that it had 
