42, MENTAL DEVELOPMENT IN ANIMALS 
method in their actions; they know they want to lead 
the intruder away from their young, not towards them ; 
and they know also when they have succeeded as much 
as they think necessary. 
Are we justified in going somewhat deeper into the 
subject and asking ourselves if such obviously intentional 
effort to deceive does not indicate the dawn of thought 
in what we are pleased to speak of as “the inferior 
animals ”’ ? 
Closely associated with this peculiarity is another 
of exceptional interest. I refer to what is termed 
““Mimicry in Nature.” This faculty, if I may so call it, 
must be regarded as of twofold character. There is that 
kind of mimicry by which an animal imitates in its form 
or colouring something quite different from itself. An 
insect, for instance, may through a series of gradations 
resemble more and more closely another insect. the 
imitation becoming almost complete in the course of 
evolution extending over a longer or shorter period. This, 
I am advised, is the case with some butterflies which are 
greedily sought after by birds, the change in their colour 
and markings being such as to give them the appearance 
of other butterflies which birds do not care for; in other 
respects the distinction between the two is rigidly main- 
tained. JI am not sufficiently acquainted with the subject 
to speak of it from my own knowledge. But we have 
many familiar instances in which insects assume the 
appearance of pieces of bark of trees which they frequent. 
On the trunks of many of our native trees insects may 
be observed which cannot readily be distinguished at 
first sight from scales of bark; caterpillars, which 
represent part of the branches, or leaves, or flowers ; 
locusts, whose colouring readily deceives even careful 
observers. Very noticeable in this class of mimetic insects 
are the so-called stick mantis, the leaf mantis, and the 
leaf butterfly. The mimetic character is found also in 
shells, crustaceans, spiders, frogs, reptiles, birds, quad- 
rupeds etc. In most cases the mimicry is acquired without 
any effort or even knowledge on the part of the imitator ; 
this may be treated .as unconscious mimicry im contra- 
distinction to that which is intentional and may therefore 
