26 THE COLOURS OF ANIMALS 



We shall see that it is common for an insect to be 

 protected by Special Resemblance at one time of its 

 life, and by General Resemblance at another, or to 

 be concealed at different periods of its life by different 

 kinds of Special or General Resemblance respectively. 



Each of these forms of Resemblance may be 

 Protective or Aggressive according as they are made 

 use of to defend from attack or to assist in capture. 

 We shall also see that Protective and Aggressive Re 

 semblances may be either Constant or Variable ; in 

 the latter case, the appearance is capable of adjust- 

 ment in order to correspond with changes in the en- 

 vironment. This, the highest form of Resemblance, 

 will be deferred until the examples of the other form 

 have been considered. 



The Larvse of Geometrse as examples of Special 

 Protective Resemblance 



There is no better instance of Special Protective 

 Resemblance than that afforded by the larvae of 

 Geometra, * stick caterpillars ' or ' loopers,' as they 

 are often called. These caterpillars are extremely 

 common, and between two and three hundred species 

 are found in this country ; but the great majority are 

 rarely seen because of their perfect resemblance to 

 the twigs of the plants upon which they feed. They 

 possess only two pairs of claspers, or legs which are 

 peculiar to the caterpillar stage, while in nearly all 



