WARNING COLOURS 197 



generally placed on an intensely black ground colour, 

 which shows them up and makes them appear to 

 project more than is actually the case. In the well- 

 known ' Hop-dog ' or * Tussock ' caterpillar {Orgyia 

 pudihunda) there are four ' tussocks,* each upon a 

 separate ring, and the furrows between these rings 

 are of the most intense velvety black. They are con- 

 cealed until the caterpillar is irritated, when the body 

 is curved in a vertical direction, so that the * tussocks ' 

 diverge, and the furrows appear as black semilunar 

 areas separating them and rendering them con- 

 spicuous. The hairs of the ' tussocks ' are so fine and 

 so closely packed that the tuft does not appear to be 

 made up of hairs at all, but to be rather a fleshy pro- 

 jection from the back of the caterpillar, and a most 

 convenient part for an enemy to seize. Fine as the 

 hairs are, they nevertheless bristle with minute lateral 

 branches, and would certainly be most unpleasant if 

 brought into contact with the skin of the mouth. If 

 seized by an enemy, the fine hairs come out in im- 

 mense numbers, and produce such an effect upon 

 the skin of the mouth that the caterpillar escapes 

 unhurt. 



The following experiment suggested the explanation 

 which has just been given. A caterpillar of the 

 Common Vapourer Moth {Orgyia antiqiia) was intro- 

 duced into a lizard's cage, and when attacked, instantly 

 assumed the defensive attitude, with the head tucked 



in and the ' tussocks ' separated and rendered as 

 10 



