450 GEORGES BOHX 



of Internal Factors on Behavior," "Habits," "Rhythms in 

 Behavior." It was with pleasure that I saw mentioned and 

 discussed some of my own researches, in particular those on 

 the temporal variations of sensibility in Cerianthus, and on 

 tidal rhythms. The following appears to me to be a very gen- 

 eral law : in proportion as external excitations are repeated or 

 prolonged, sensibility at first increases and later diminishes, the 

 first phase being shorter as the organism is less rich in certain 

 active substances. One gets a glimpse here of the interest which 

 attaches to physico-chemical explanations, w r hich Holmes does 

 not reject, but of which he takes little account, no doubt because 

 they are still a little premature. On the subject of rhythms, I 

 should like to remark that there are strong rhythms and weak 

 rhythms ; the latter may be easily masked by the causes actually 

 in operation, and great precautions, which certain authors 

 (Morse in particular) have failed to take, and which I have 

 indicated in my articles (sensibilisator, maintenance of constant 

 illumination and hygrometric state, etc.) are necessary to demon- 

 strate their existence. I shall not revert to the pleasure -pain 

 theory, of which I have spoken above and which is well known 

 to the readers of this review, since it was set forth at length by 

 its author in the Journal of Comparative Neurology and Psy- 

 chology for 1 910. With pleasure-pain reactions intelligence came 

 into being. Holmes justly rejects the old opposition of instinct 

 to intelligence : there are already present along with instinct 

 the rudiments of intelligence when the animal profits by experi- 

 ence through the formation of associations; from simple associa- 

 tive memory it is possible to pass through all the intermediate 

 stages to the complicated forms of reasoning. These are the 

 views which I also have maintained in my books, "La Naissance 

 de 1 'Intelligence" and "La Nouvelle Psychologie Animale." 



In the following chapters (IX to XIII), Holmes seeks to show 

 us the evolution of intelligence ; with Bethe, Spaulding, and A. 

 Drzewina, he presents to us the primitive forms of intelligence 

 in crustaceans and molluscs, and discusses the intelligence of 

 insects, lower vertebrates, mammals, and, lastly, the monkeys. 

 In treating of the mammals, he insists on the necessity of ex- 

 periments: he discusses in particular those of Thorndike, his 

 imitators and pupils. But experiments should be conducted 

 with discrimination, and caution must be observed in drawing 



