40 K. S. LASHLEY 



hence severed any direct connections which may have existed 

 between areas on opposite sides of the lesions. Text figure 7 

 is a composite diagram showing by straight lines the long 

 axes of the lesions in those animals which made not more than 

 five errors in retention tests. In every case included in the 

 diagram tissue probably intact and functional in the visual 

 habit lay on each side of the lesion, so that the lines represent 

 planes of section between functional areas involved in the 

 habit mechanism. In the entire series the occipital cortex was 

 divided in a great variety of planes and, in one case or 

 another, almost every possible part of the area was isolated 

 from other parts. Yet in these cases the retention of the 

 habit was but little affected. Thus it appears that the cere- 

 bral mechanisms of the habit can function normally and can 

 exert their mutual reinforcement in spite of the destruction 

 of any particular group of cortical association fibers within 

 the area, provided only that the divided portions of the area 

 retain some connection with the remainder of the cortex or 

 with subcortical structures. This means either that the facili- 

 tation is exerted solely upon centers centrifugal to the occipi- 

 tal area through a common termination of discrete paths 

 from that area or that the cerebral mechanism is of such a 

 character that facilitating impulses between neighboring 

 areas may traverse any anatomical bridge which happens to 

 remain intact. 



In previous discussions of equipotentiality of areas within 

 the cortex I have assumed reduplication of parts as the 

 simplest hypothesis to account for it. That is, the muscular 

 contractions involved in the performance of the habit might 

 be initiated by impulses coming over reflex paths which are 

 scattered uniformly throughout the functional area and im- 

 pinge on the same final common path. A small lesion might 

 then destroy a part of these paths, but leave enough intact 

 to carry out the function. Mutual facilitation of such redu- 

 plicated paths might furnish a mechanism for the mass action 

 of the visual area, but certain aspects of the present data 

 throw some doubt upon this and suggest a different interpre- 

 tation of the facts. 



