HOLMES'S THE EVOLUTION OF ANIMAL INTELLIGENCE 449 



possibility of choice in the infusoria. According to Mast, who 

 is here in essentials repeating an opinion of Maupas's (expressed 

 in my " Naissance de 1' Intelligence"), the choice is only appar- 

 ent, and is due, for example, to the fact that the prehensile 

 organ adheres to certain organisms and not to others. But 

 Metalnikow has just shown that if the infusoria do not in general 

 choose their food, they can at least learn to choose it. 



With Chapter V the discussion on instinct begins. Holmes 

 recalls the fact that I have regarded " instinct " as a word adapted 

 merely to hand down to us certain old notions which nourished 

 before the introduction of experimental analysis in comparative 

 psychology. He himself is a partisan of the conservation of 

 this word. The animal, he justly observes, is not merely a 

 machine which responds to the various influences of the environ- 

 ment : it possesses an innate stock of impulses, which lead it 

 to act in a definitely determined manner, independently of 

 stimulations from the surroundings. From the beginning of 

 its life, we must take account of internal impulses (the Triebe 

 of the German writers). Instinct represents this innate stock 

 of impulses: to keep the notion of instinct means to show that 

 we do not fail to recognize the importance of internal states, of 

 internal factors. In other respects, the activities determined by 

 internal factors do not differ fundamentally from the activities 

 called reflex. The stimuli are internal instead of external. 



Holmes speaks of the "marvellous adaptation" of instinct; 

 yet he recognizes that in many cases it is far from being perfect, 

 and he shows us instincts which are in process of perfecting and 

 evolving (Chapter VI). 



Two very interesting chapters are VII and VIII, which treat 

 of "Non-intelligent Modifications of Behavior," and of "The 

 Pleasure-pain Theory." According to Holmes, even among the 

 lower organisms there is a sort of auto-regulation of actions, 

 which leads to adapted responses: these responses have con- 

 tributed to the development of intelligence, which in its turn 

 has had its full expansion when the adaptations have become 

 much more varied through the perfecting of the formation of 

 associations. Many facts bearing on this subject are set forth 

 in a series of paragraphs entitled: "Action of Combined Stim- 

 uli," "Diminution of Reaction to Repeated Stimulation," 

 "Different Kinds of Response to a Given Stimulus," "Influence 



