CORTEX AND CORPUS STRIATUM 97 



female may mate, lay fertile eggs, incubate them, and 

 rear the young. In these birds there is greater tend- 

 ency to a fixed type of reaction. Thus the male will 

 give the courting and fighting reaction to any small 

 moving object, but only while it is moving. There is 

 no spontaneous fighting of an object or bird which is 

 not moving. Fear reactions and efforts to escape 

 from confinement are absent and there is no spontane- 

 ous flight of escape when the bird is unconfined by 

 a cage. Avoiding reactions of flight can be induced by 

 mistreatment (strong stimulation), but not by mov- 

 ing objects which do not touch the bird. Reactions 

 are more readily fatigued than in the normal bird. 



These observations apply to birds kept for three 

 to six months after operation. It is concluded that 

 physiologically the cortical part of the hemispheres 

 is related to the production of a greater variety of 

 reactions from a single stimulus; to the lowering of 

 the threshold for distant stimuli; to the exercise of an 

 augmentor effect so that the reactions are more pro- 

 longed and persistent. Apparently, the pigeon's cor- 

 tex is so incompletely separated from the striatum 

 and of so low an order of differentiation that its defect 

 can in large part be compensated by the underlying 

 tissue. These conclusions are significant and must 

 be kept in mind when we come to consider the much 

 better developed cortex of the lower mammals. 



Progressive removal of the corpus striatum, from 

 without inward, results in loss of successive phases of 



