300 ANIMAL DEFENCES 



niitralis) which when at rest might readily be mistaken for a 

 projecting knot, while other sorts have been described in which 

 splashes of birds' excrement are faithfully copied. 



The foregoing examples will perhaps suffice to illustrate pro- 

 tective resemblance more or less constant in kind to special 

 objects, and a few instances will now be given of the somewhat 

 rarer phenomenon of variable resemblance of the same kind. 



Variable Special Protective Resemblance. — So far as the 

 species is concerned, the Leaf- Butterflies i^Kallima) already 

 described might very well be placed here, for there is great 

 variability in the colouring of individuals, just as there is among 

 the dead leaves to which the colours give resemblance. But cases 

 are also known where the same individual is capable of altering its 

 appearance so as to copy, as it were, more than one sort of ex- 

 ternal object. The power of doing this is suspected in far more 

 numerous instances than those for which it has actually been 

 proved, but Poulton (in The Colotirs of Animals) gives a strik- 

 ing and unequivocal example in the stick -caterpillar, which is 

 the larval stage of the Early Thorn Moth {Selenia ilhmaria), 

 a native species. When resting on a brown twig this cater- 

 pillar conceals itself in the way already described for a similar 

 form, but when feeding upon a green leaf that method would 

 be impossible. Yet by throwing its body into several sharp 

 kinks, and remaining motionless, it assumes a resemblance to a 

 shrivelled bit of dead leaf or some other object such as might be 

 expected to occur on the foliage. 



We have now discussed at some length cases of precautionary 

 measures (see p. 276) depending upon bodily characteristics which 

 make for inconspicuousness, and we must now turn to instances of 

 precisely opposite kind, where bodily characteristics make their 

 possessor very conspicuous. 



