574 KARL T. .WAUGH 



greater ease of jumping off, #hich had been acquired through 

 practice. 



The disk with its supporting column was inverted and inserted 

 in the bench-top from below. This was done because it was feared 

 that the animal in peering over the edge of the disk might be 

 influenced by seeing the column. A large plate of glass was fixed 

 under the disk in its new position. 



With, disk inverted and (/lass below it 



At 4 cm. the vibrissae touched the glass. D's average, even 

 at this height, was unusually long. 



When the glass was lowered to a distance of 10 cm. above the 

 floor the results were similar to those just presented. 



With a board, instead of tln> glass, placed below the disk 



MOUSE (i CM. 5 CM. 4 CM. 3 CM. !> CM. 



sec. sec. -tec. sec. sec. 



I" 120 32 22 



I (2d scries) 75 31 17 



.\<l 120 120 45 36 2 



XI) 120 120 120 5 



Xc 120 69 10 



Xc (2d scries) 60 33 



T 120 59 32 



The effect of a white and black bench surface upon the animal's 

 reactions was next tested. 



Method: With the disk in position above the bench, white 

 and black papers were spread over the bench in such a way that one 

 half of the disk was above white, the other half above black paper. 

 A large piece of plate glass having a round hole in the center for 



