176 ANIMAL LIFE 



skin. As there are certain rules of composition in 

 painting, certain old proprieties to be observed, which 

 taste has evolved and custom obeys, so there are 

 certain lines along which the skin-painting of the 

 prawn begins ; certain areas along the back and 

 breast and across the body along which the invisible 

 hand first works before filling up the canvas. 



In such a fashion the resemblance between the 

 prawn, Hippolyte, and its surroundings is produced. 

 Its pigments, primarily organs of nutrition, and still 

 subserving this function, are controlled both from 

 within by the nervous system and from without 

 by the light. So long as the larval Hippolyte drifts 

 from place to place through the offshore waters there 

 is no contrast of light and shade that can effect any 

 continuous action ; when the tide carries it to the 

 shore it is as a still, colourless, week-old, tiny prawn 

 that it clings to the first holdfast. But once it comes 

 to rest in the submarine forest the contrast of light and 

 shade begins to work a sea change. Its pigments 

 develop, watched over by the eye, encouraged by 

 shade, discouraged by brightness. First along certain 

 tracts that form the easily followed lines of composi- 

 tion, and then filling up the shadows, leaving the high 

 lights to render themselves by untouched canvas, 

 or at most by a sparing use of yellow and white, Hippo- 

 lyte is all unconsciously following the best traditions, 

 and unwittingly, Ulysses-like, making itself a part 

 of all it encounters. 



Beyond the power to follow a helpful traditionary 



