PROTECTIVE RESEMBLANCES IN LEPEDOPTERA 33 



angular zigzag (e.g. Selenia illunaria; see fig. 8), thus 

 resembling a dead and crumpled piece of leaf, or the 

 spiral leaf-case made by other insects, or the excre- 

 ment of birds or snails. The caterpillar of Selenia 

 illunaria has a very similar structure and colouring 

 at the times when it resembles such very different 

 objects as a twig and the excrement of a bird, the 

 whole difference being made by a modification of atti- 

 tude alone (compare figs. 4 and 8). I have seen the 

 larva of the Brimstone Moth twisted into a spiral, 

 resting motionless close to the 

 notch which it had eaten out of 

 a leaf ; in this position it forcibly 



suggested the appearance of a *. 8 -- Th e you 



Early Thorn ( 



small piece of leaf which had 



been accidentally torn, and had 



turned brown and curled up, remaining attached to 



the uninjured part of the leaf by one end. 



We may well suppose that the acquisition of a 

 form and attitude which lend themselves so readily to 

 the purposes of concealment, was very advantageous 

 to the ancestral Geometra, and enabled them to spread 

 over the vegetable world, dividing into an immense 

 number of species, and ousting many larvae with less 

 perfect methods of concealment. In their widening 

 range certain Geometrce have thus come to feed upon 

 low-growing plants which are altogether without twigs 

 or branches. The attitude is then modified, and sug- 

 gests some object which might be expected to occur 



