64 HANDBOOK OF BRITISH INLAND BIRDS 
When we see that the practice of adding lichens 
actually tends to endanger the nest twice out of 
three times, it is scarcely reasonable to suppose 
that the lichens are added in the third case for 
the definite purpose of concealing it. Protective 
mimicry is undoubtedly one of the forces which 
have a great influence in the life-history of birds 
and animals and insects ; but the more carefully we 
examine the question the more we seem to see that 
it is after all only one of many such forces, most 
of which we have not yet perceived and under- 
stood ; and there has been a tendency of late years, 
which has spread from learned scientific treatises 
into the most popular text-books, to apply this 
" protective mimicry " theory to many cases where 
it is not supported by the general body of the 
facts. To return to the Long-tailed Tit's nest, 
which has led us off into one of the questions 
which most constantly suggest themselves as we 
watch our bird-life at first hand, beneath the 
lichens it is mainly built of moss, and is thickly 
lined with feathers. It is built up from the 
bottom, and in its early stages is often exactly like 
a half-built Chaffinch's nest. Then the sides are 
carried up, first evenly, and then one side faster 
than the other ; this side is finally continued over 
the top, like a hood, and the entrance-hole is formed 
a little below it. Seven or eight eggs are usually 
