30 



THE COLOURS OF ANIMALS 



continuous with it (see fig. 7, page 31). Between the 

 two pairs there is necessarily a furrow, where the body 

 of the larva lies along the cylindrical branch. This 

 furrow, which, if apparent, would greatly interfere with 

 the resemblance, is rendered inconspicuous in the fol- 

 lowing manner. The under side of the caterpillar is 

 somewhat flattened, so that it is in contact with a 

 small part of the circumference of the branch, and 

 the furrow on each side is partially filled up, at any 



rate in certain species, by a number of fleshy tubercles. 

 The shadow which would betray the furrow is also 

 neutralised by the light colour of the tubercles. The 

 effect will be clear on comparing a, b, and c in fig. 5 : 

 a is a section of a branch just below the point where 

 a lateral twig comes off ; 6 a diagrammatic section of 

 a branch and the caterpillar's body ; c the same with 

 the addition of the tubercles, which render the outline 

 more like that of a. 



I will illustrate the extraordinary degree of resem- 



