44 MENTAL DEVELOPMENT IN ANIMALS 
that the under surface of its wings resembles a dead leaf ; 
nor does there seem to be any suggestion of design in the 
attitude it takes up. That is one of the habits of its life, 
and if it had no leaf-like marking, the position it places. 
itself in would probably be the same. The protective 
colouring and altitude combined have resulted, no doubt, 
from the fact that they have saved its progenitors, when 
others of its kind have fallen a prey to their hungry enemies. 
It is a case of the survival of the fittest, which, continuing 
with slight variations through generation after generation, 
has at last become almost identical in appearance with 
the object imitated. This interpretation of the 
phenomenon, inferential though it necessarily is, has now 
been generally accepted. 
One case of conscious mimicry I have already touched 
upon in the beginning of this paper. I have observed some 
very marked instances of this kind among the smaller 
birds which live hy the sea, and lay their eggs in the drift 
which accumulates just above the high-tide line. Some 
of these have that mimetic colouring which I have 
referred to as unconscious : so much so indeed that as they 
sit upon their eggs they may be passed within a few yards 
without exciting notice. In some cases their eggs are 
mimetic in their colouring, while the young chicks are brown 
in colour and marked with stripes of a darker shade, 
which extends from the neck lengthways along the body. 
The effect of this is that when the parent bird by her 
pretences has induced intruders to follow her away from 
her young, these can more readily conceal themselves. 
The eggs of plovers, including the stone plover, or curlew 
as it is commonly called, are similarly marked, as are also 
the chicks, while the mother plover is an admirable 
pretender. 
In the case of other animals, the mimicry assumes 
another form. Many spiders bear a very marked resem- 
blance to the plant they consmonly frequent, and some 
of these construct snuggeries for themselves by so twisting 
a leaf that its two edges meet ; they then bind these 
together with their web. I wish, however, more particularly 
to refer to our trap-door spider (atrax robustus), a specimen 
of whose nest with the trapdoor attached was brought 
