184 ANIMAL LIFE 



is further heightened by the stumpy legs of the cater- 

 pillar, which recall the irregularities of the twigs. In 

 some cases the colour varies, so that, as in Hippolyte, 

 light and dark, plain and variegated forms of the 

 same caterpillar are found, in each case agreeing 

 with the colour of the foliage and the markings that 

 occur upon it. In such sensitive larvae the same 

 influences are at work in producing the sympathetic 

 colouration as are active in calling forth the agreement 

 between the colour-varieties of the prawn and its 

 weed. In both cases a dim light encourages the 

 development of pigment and the formation of a dark 

 variety ; a bright light has the reverse effect ; but in 

 the caterpillar the change takes place more slowly, 

 and is less controlled by the influence of sight than 

 in the prawn. In both it is the early stages of develop- 

 ment that are chiefly and most rapidly susceptible 

 of modification by the light reflected from their sur- 

 roundings, but whereas this power persists throughout 

 the life of the prawn, it is lost and the colouration 

 rendered permanent before the caterpillar has attained 

 its full size. 



Amongst butterflies and moths there are many 

 instances of the same sympathetic or cryptic coloura- 

 tion. Obvious as these animals are upon the wing, 

 they often disappear as if by magic when they come 

 to rest. The buff-tip moth rests motionless by day 

 upon tree-trunks, and the yellow patch at the tips of 

 its forewings looks precisely like the coloured end of 

 a broken twig. The hair-streaks, which often hover 



