PLAY AND INSTINCT. 61 



acquired movement, pass through the cerebrum. In- 

 stincts and reflexes, however, have their seat for the 

 most part elsewhere. The tracts of very few of them 

 are found in the cortex of the hemispheres. It is chiefly 

 in the lower parts of the brain and spinal cord that the 

 associations and co-ordinations corresponding to in- 

 stincts and reflexes have their seat. When the compara- 

 tive anatomist investigates the relative size of the hemi- 

 spheres in vertebrates (especially in amphibians, rep- 

 tiles, birds, and mammals), a very evident increase in 

 size is observed which apparently goes hand in hand 

 with the gradual gain in intelligence. In the course of 

 long phylogenetic development, during which the hemi- 

 spheres have gradually attained their greatest dimen- 

 sions, they have constantly been the organ of reason and 

 the seat of acquired association. If, then, habit could 

 become instinct through heredity, it is probable that the 

 cerebrum would in much greater degree than is the fact 

 be the seat of instinct." * 



But what part has psychology had in this war of 

 opinions? It is impossible for her to give a satisfactory 

 answer to this question. She must pick her way cau- 

 tiously, and in the matter of instinct the adoption of 

 the neo-Darwinistic theory is evidently the most prudent 

 course, for to it belongs the now universally recognised 

 principle of selection. Accordingly, when I speak of 

 instinct it will be in accordance with this idea of innate 

 hereditary variations, passing by the Lamarckian theory 

 as either obsolete or a point of view yet to be substanti- 

 ated. In what follows I adhere in essentials to the defi- 

 nition that Ziegler, a follower of Weismann, has given in 



* H. E. Ziegler, Ueber den Begriff des Instincts, Verh. d. 

 deutsche zool. Gesellschaft, 1891, p. 134. See also Baldwin, Men- 

 tal Development in the Child and the Race, chap, yii, § 4. 



