PEOTECTIVE RESEMBLANCES DIMORPHISM, ETC. 43 



dark brown, so that the caterpillar harmonises well 

 with the colour of its new surroundings. The sig- 

 nificance of this change was first pointed out by 

 Professor Meldola. Other nearly allied caterpillars 

 feeding upon trees, such as willow or poplar, which 

 grow in damp situations where the ground is covered 

 with green vegetation, do not turn brown to anything 

 like the same extent. 



A very interesting instance of exactly the opposite 

 change at a corresponding period is afforded by the 

 caterpillar of the August Thorn Moth (Ennomos angu- 

 larid), a brown ' stick caterpillar,' protected by a very 

 perfect Special Eesemblance to the dark twigs of the 

 elm on which it feeds. When full-fed it constructs a 

 very loose cocoon of elm leaves, so loose and open that 

 it is easily seen within, and its brown body would be 

 conspicuous against the background of green leaves. 

 But at the same time the dark brown colour of its 

 surface entirely disappears, and the animal is tinted 

 by its green blood, which is seen through the trans- 

 parent skin ; it is thus well concealed by General 

 Resemblance to its new surroundings. 



Another exceedingly interesting case of the same 

 kind of change is witnessed in the caterpillar of the 

 Miller Moth (Acronycta leporina), which sits motionless 

 on the under side of the leaves of the birch and alder, 

 and is covered with very long beautiful hair which is 

 brilliantly white, and bends over on all sides so as to 

 touch the leaf, forming a wide margin round the 



