146 The Outline of Science 



The leaf -butterfly Kallima, conspicuously coloured on its 

 upper surface, is like a withered leaf when it settles down and 

 shows the under side of its wings. Here, again, there is precise 

 form-resemblance, for the nervures on the wings are like the mid- 

 rib and side veins on a leaf, and the touch of perfection is given in 

 the presence of whitish spots which look exactly like the discolora- 

 tions produced by lichens on leaves. An old entomologist, Mr. 

 Jennei Weir, confessed that he repeatedly pruned off a 

 caterpillar on a bush in mistake for a superfluous twig, for many 

 brownish caterpillars fasten themselves by their posterior claspers 

 and by an invisible thread of silk from their mouth, and project 

 from the branch at a twig-like angle. An insect may be the very 

 image of a sharp prickle or a piece of soft moss ; a spider may look 

 precisely like a tiny knob on a branch or a fragment of lichen ; one 

 of the sea-horses (Phyllopteryx) has frond-like tassels on various 

 parts of its body, so that it looks extraordinarily like the seaweeds 

 among which it lives. In a few cases, e.g. among spiders, it has 

 been shown that animals with a special protective resemblance to 

 something else seek out a position where this resemblance tells, 

 and there is urgent need for observations bearing on this selection 

 of environment. 



5 

 Mimicry in the True Sense 



It sometimes happens that in one and the same place there are 

 two groups of animals not very nearly related which are "doubles" 

 of one another. Investigation shows that the members of the 

 one group, always in the majority, are in some way specially pro- 

 tected, e.g. by being unpalatable. They are the "mimicked." The 

 members of the other group, always in the minority, have not got 

 the special protection possessed by the others. They are the "mi- 

 mickers," though the resemblance is not, of course, associated with 

 any conscious imitation. The theory is that the mimickers live on 

 the reputation of the mimicked. If the mimicked are left alone 



