METHODS OF STUDYING VISION IN ANIMALS 



23 



ings differ in form while being equal in area. They are (a) the 

 6 cm. circle; (b) a hexagon 3.299 cm. on the side; (c) a square 

 5.317 cm. on the side; (d) and an equilateral triangle 8.081 cm. 

 on the side. The area of each opening is 28.2743 sq. cm. In 



TABLE 3 



Description of Standard Stimulus Plates. Each Plate 

 IS A 12 CM. square of i-i6 inch Acid Blackened Brass, 

 Containing an Accurately Cut and Centered Opening. 



Description of Openings 



To test 



Form 



Perception 



Equil. 

 triangle 



8 .081 cm. 



Openings inscribed in 6.000 cm. circle 



Hexagon 3 . 000 cm. 23 . 382 



Square 4.243 cm. 18.003 



Equil. 



triangle 5.196 cm. 11. 691 



Total 



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