COLOR IN ANIMALS 141 



and usually rests on the twigs of its food-plant. The dark 

 color is still present on the back but is softened to a purplish 

 tint, which tends to be replaced by a combination of white 

 and green in many of the largest larvae (Plate 78, D\ Such 

 a larva is well concealed by general protective resemblance, 

 and one may search a long time before rinding it, although 

 assured of its presence from the stripped branches of the 

 food-plant and the fceces on the ground beneath. 



" As soon as the larva is discovered and disturbed it with- 

 draws its head into the first body ring, inflating the margin, 

 which is of a bright red color. There are two intensely 

 black spots on this margin in the appropriate position for 

 eyes, and the whole appearance is that of a large flat face 

 extending to the outer edge of the red margin (Plate 78, D). 

 The effect is an intensely exaggerated caricature of a verte- 

 brate face, which is probably alarming to the vertebrate ene- 

 mies of the caterpillar. The terrifying effect is therefore 

 mimetic. The movements entirely depend upon tactile 

 impressions: when touched ever so lightly a healthy larva 

 immediately assumes the terrifying attitude, and turns so as 

 to present its full face toward the enemy ; if touched on the 

 other side or on the back it instantly turns its face in the 

 appropriate direction. 



" The effect is also greatly strengthened by two pink 

 whips which are swiftly protruded from the prongs of the fork 

 in which the body terminates. The end of the body is at 

 the same time curved forward over the back (generally much 

 further than in the figure), so that the pink filaments are 

 brandished above the head." 



Experiment showed that the terrifying attitude and mo- 

 tions were effective in frightening away enemies. I suspect 



