BEHAVIOR OF VERTEBRATES 449 



lines, and another to discriminate the thiity mm. from the 

 fifty mm. circle . In testing for the threshold of form discrim- 

 ination he found that one animal probably distinguished between 

 two rectangles of twenty by thirty mm. with their long axes 

 respectively horizontal and vertical, although forms more widely 

 different (square and ciicle) were not distinguished. 



Washburn and Abbott (28) in a carefully controlled research 

 show that the rabbit can discriminate between the Bradley 

 saturated led paper and Hering's grey Nos. 7, 14 and 15. Caie 

 was used to show that the discrimination was made in visual 

 teims. Red was found to have a distinctly low stimulating 

 effect. One series of experiments show discrimination between 

 Hering's velvet black and Bradley saturated red, although 

 some experiments carried out to test this latter conclusion fail 

 to confirm the first set of experiments. The authors do not 

 maintain that the above discriminations were made on any 

 other basis than that of brightness difference. 



The results obtained with saturated blue are not decisive; 

 the animals, though, regularly distinguished it from Stoelting 

 black. Here, too, the discrimination was probably made in 

 terms of brightness. Several experiments tend to show that 

 the brightness equivalent of the blue probably lies around 

 Hering's grey No. 7. The authors hold that they have obtained 

 some evidence to show that the rabbit is able to form the habit 

 of choosing the darker of two impressions, irrespective of their 

 absolute brightness. It is probable that the rabbit, while cap- 

 able of using binocular vision, uses monocular more commonly. 



Smith (24) tested the color responses ot dogs. The tests 

 were carried through completely only on one dog. The appara- 

 tus consisted ot a large box suitably divided into home and 

 trial compartments. Five shutters, each of which when pulled 

 upward disclosed an opening for the exit of the animal, carried 

 the stimulus. Food and punishment (consisting of electric 

 shocks) were used as motives. 



The principal stimuli employed were the Zimmermann col- 

 ored papers; the most saturated red, blue, gieen, yellow, ma- 

 genta and orange (Nos. c, o, k, g, a). The color work was con- 

 trolled by the use oi achromatic stimuli. For this latter work 

 Nendel's greys were employed. 



The authoi concludes that while certain of the dogs do pos- 



