HABIT FORMATION IN THE ALBINO RAT 7 



circular maze. This maze has a wooden base one hundred and 

 fifty centimeters in diameter and six aluminum runways fifteen 

 and five tenths centimeters high and ten centimeters wide. 

 The entrances to the alleys are ten centimeters wide, and are 

 at alternate ends of a quadrant arc. The radial stops in alleys 

 1 to 5 are also placed at alternate ends of a quadrant arc, the 

 stop in each alley being directly opposite its entrance. Thus, 

 it is possible for a rat to run only one half the circumference 

 of a runway in either direction before being forced to turn. 

 This is not true of alley 6, where no stop is employed. The 

 central circle, or food compartment is twenty centimeters in 

 diameter. A three quarter inch mesh wire top prevents the 

 animals from escaping, without interfering with observations of 

 their movements. The camera lucida attachment consists pri- 

 marily of two mirrors and an achromatic lens. The arrange- 

 ment is as follows: A large plate glass mirror is fastened by 

 supporting framework at an angle of forty-five degrees, with its 

 center directly above and one and eight tenths meters from 

 the center of the maze. A somewhat smaller mirror is placed 

 facing the first and making an angle of ninety degrees with it 

 at such a distance away that the light reflected downward falls 

 outside the niaze area. In the path of this reflected light is 

 placed a single achromat six centimeters in diameter and of 

 fifty centimeters focus in a mounting provided with rack and 

 pinion adjustment which is fitted into the center of a wooden 

 disc thirty centimeters in diameter. Below this at the focus of 

 the lens is placed a second wooden disc of the same diameter as 

 the first, which serves as a holder for the paper upon which 

 the image of the maze is reflected. Both of these discs are 

 attached to iron collars which slide independently up and down 

 the rod CR, thus making it possible to vary the size of the 

 image. A small curtain of dull black velvet attached to the 

 upper disc serves to exclude all extraneous light from the re- 

 cording table and as a further aid in sensitizing the eye, a large 

 curtain of dark material encircles the space occupied by lens 

 and recording apparatus as well as the experimenter's chair. 

 This curtain also serves the purpose of completely hiding the 

 experimenter from the animals while they are running in the 

 maze. 



