n] HABITS OF CONVOLUTA 45 



and-heat stimuli, large numbers of C. roscoffensis are 

 placed in sea-water contained in a long glass trough, 

 the axis of which is parallel with the direction of the 

 light. Promptly, the animals mass themselves at the 

 end of the vessel directed to the light. The water 

 at that end is heated gradually ; but in spite of the 

 rising temperature, and in spite of its powers of 

 negative thermotropism, Convoluta remains faith- 

 fully at its light station, and dies in thousands at its 

 post. Habitual obedience to the command of light 

 renders it oblivious of the warning of increasing 

 temperature, which warning suffices to bring about 

 the withdrawal of less pre -occupied animals from 

 dangerous regions. We see in the behaviour of the 

 plant-animals thus subjected to simultaneous stimu- 

 lation not an illustration of the inevitableness of a 

 reflex, but an example of the limitations attaching 

 to all nervous actions, both reflex and conscious. 



The behaviour of C. roscoffensis with reference 

 to black and white backgrounds supplies a striking 

 illustration of the fact that circumstances alter re- 

 flexes. These "background" responses we will now 

 consider. The choice of a definite background is a 

 phenomenon exhibited by many sea-shore and aquatic 

 animals. When offered the alternative of a white or 

 black background, some animals take up a position 

 on the one, some on the other. Thus among the 

 marine Crustacea, certain prawns and also species of 



