136 ANIMAL LIFE 



live with light, water, and air. A plant moves towards 

 the light, its roots track the watercourses, its leaves 

 respond to the quality of air, because in these acts it 

 finds the materials for food and new life. In the same 

 way these old responses form the basis for animal 

 actions. In them the senses are not emotions or per- 

 ceptions apart. They are invariably bound up with 

 a movement or adjustment which has to do with the 

 preservation of life ; and these adjustments are no new 

 acquisition, but are traceable in the humblest living 

 thing. The origin of instincts has been needlessly 

 obscured by overlooking the fact that * sense ' is only 

 a link in a chain of action, and also by treating organs 

 of sense as things apart, instead of regarding them as 

 inseparably linked with essential adjustments. 



The Senses of Shrimps. Instincts are combinations 

 of these old responses. We may take a shrimp as an 

 example. By day we see it lying motionless in the 

 sand or clasping a branch of seaweed. By night we 

 find it swimming with great vigour at the top of its 

 prison-water, its heart and breathing organs beating 

 at a great rate, its colour altered from brown to blue, 

 and its nervous system extremely highly strung and 

 sensitive to shock. At the least alarm it will now 

 leap out, whereas by day no ordinary disturbance 

 would cause it to forsake its chosen spot. The tone 

 of its being has been altered, and after persisting 

 through the night this agility will give place at day- 

 break to the more sluggish habit of its sleeping hours. 

 In recording the behaviour of an animal, therefore, we 



