38 THE INFLUENCE OF ENVIRONMENT ON 



nearly all the light, and therefore reflects little or 

 none, will stimulate the eye to a very faint extent, 

 and hence cause a very feeble current, if any at all, 

 and so the chromatophores will remain unstimulated, 

 and as in the case of the blind fish, the fish will 

 remain dark. On the other hand, light from a 

 red or blue object will cause a current of rather 

 greater intensity, and will cause the brown or 

 red chromatophores to expand, and so more or 

 less conceal the black ones. Finally, yellow 

 light will cause the strongest stimulation and all 

 the chromatophores will give out processes ; the 

 yellow ones, being most superficial, will be the 

 most conspicuous, and will hide the deeper and 

 darker ones to a greater or less extent. 



In the foregoing remarks I have endeavoured to 

 show, first in a general way, and afterwards by the 

 consideration of a few selected examples, that the 

 relation between an animal and its environment 

 is a very definite and direct one, and in many cases 

 a calculable one. 



We have seen from certain special cases that an 

 organism responds promptly and with certainty 

 to certain changes in its environment. Can we 

 not extend this and speak of the actual structure 

 of an animal as the resultant of the various forces 

 acting on it, both external and internal ? Small 

 changes in environment seem to give rise to results 

 altogether disproportionate with themselves ; but 

 then we must remember that the bodies of animals 

 are of very complex chemical composition and in 

 very unstable equilibrium, and in such cases a 



