238 Journal of Comparative Neurology and Psychology. 



of this fact that has shaped my experimental work during the past 

 five years, and that now leads me to offer the following results of 

 my study of the dancer primarily as a contribution to the evolution 

 of method and as an aid to the profitable formulation of problems. 



This paper is a direct continuation of the studies in the behavior of 

 the dancer which are described in my book, "The Dancing Mouse."^ 

 Although I have attempted so to write the paper that both methods 

 and results shall be intelligible to those readers who are not familiar 

 with the details of previous publications,^ it has been necessary — in 

 order to keep my account within reasonable space limits — for me to 

 omit everything except the chief points, in connection with methods 

 which I have previously described, and a concise statement of new 

 results. In other words, I have been forced to assume much more 

 knowledge on the part of the reader than I should if this were my 

 first publication on the subject. 



Certain problems concerning the relation of age and sex to 

 habit-formation which were proposed in my book, and either left un- 

 solved or only partially solved, are brought nearer to satisfactoi'v 

 solution by the results herein reported, and a multitude of new prob- 

 lems are revealed. To me, however, the investigation presents itself 

 simply as another step toward a realization of the complexity of the 

 phenomena of behavior and of the need for accurate analytic methods. 



II. RELATION OF AGE AND SEX TO RAPIDITY OF ACQUISITION 

 OF A VISUAL DISCRIMINATION HABIT. 



Can the dancer acquire a given habit with the same rapidity at 

 different ages ? This question was the starting point of a study of 

 plasticity which has already been reported in part.^ Before present- 

 ing the results of my experiments I shall very briefly, with the help of 

 figures which are reproduced from an earlier paper, describe the 

 method of work. 



'Yerkes, Robert M. The Dancing Mouse : a study in animal behavior. New 

 York, The Macmillan Company, 1907. xxi + 290. 



'Yerkes, Robert M. and Dodson, John D. The Relation of Strength of 

 Stimulus to Rapidity of Habit-formation. Jour, of Comp. Islcur. and Psy., vol. 

 18, p. 459-482, 1908. 



•The Dancing Mouse, pp. 270-215. 



