BODILY CHARACTERISTICS— INCONSPICUOUSNESS 293 



perfect manner with the weeds among which they happen to be 

 found, green, red, or brown as the case may be; and further, that 

 individuals adapted to Hve among weed of one colour are able 

 to adjust their appearance, though not very rapidly, to surround- 

 ings of new form and colour. There is further a quick response 

 to alterations in the intensity of light. But beyond this there is 

 a remarkable periodic colour-change, corresponding to the alter- 

 nations of day and night, the utility of which is not at present 

 known. To quote the above-named authors: — "Every evening, 

 as darkness comes on, Hippolyte gradually loses its distinctive 

 diurnal colour. In summer the change begins at about 9 p.m., 

 in winter at about 5 p.m. Towards this or that time, according 

 to the season, a reddish tint — a sunset glow — the foreshadowing 

 of the change, makes its appearance. This is followed by a green 

 tinge which spreads fore and aft from the middle of the body. 

 The green colour gradually melts into blue, and a general increase 

 of transparency sets in. Thus, as darkness falls, Hippolyte is 

 seen to become of a wonderful azure -blue colour and absolutely 

 transparent, except in the region of the liver and stomach, which 

 are now very clearly visible. The depth of the blue colour varies 

 in different specimens; in some it is almost indigo, in others the 

 faint azure of a sky at sunset." The changes in hue depend upon 

 the condition of branching colour-bodies which are present. These 

 contain various pigments, the distribution of which can be varied 

 as the result of the action of light and other agents, that work 

 in part through the agency of the eyes and nervous system, and 

 in part independently of these. 



Colour-Change in Insects. — The subject of variable pro- 

 tective resemblance must be concluded by referring to some 

 extremely interesting cases presented by Insects in the various 

 stages of their life-history. Numerous instances are known where 

 caterpillars of the same kind vary in colour according to the hues 

 of their surroundings. This may be illustrated by an experiment 

 of Poul ton's conducted on the larvae of the Peppered Moth 

 i^Amphidasis betidarid). A large batch of eggs taken from the 

 same individual was divided into two parts, one half being then 

 hatched out among the green leaves and shoots of birch, and 

 the other among dark-brown twigs of the same plant with a 

 certain admixture of leaves. All the caterpillars of the former 

 half were bright-green, while the large majority of the other 



