514 ADAPTATIONS TO PHOTIC QUALITY 



preliminary report, seems a truly model investigation. She reported, in 

 1933, on three Sciurus vulgaris, which she had trained with red, blue, 

 yellow, and green papers and with the Hering series of 30 grays. The 

 first animal was trained positive to red versus gray, and proved unable to 

 discriminate red from any dark gray. Substitution of another gray for the 

 red produced no disturbance in the sensitive creature, indicating that the 

 squirrel sees red objects as gray. It would go to the darker of two grays, 

 and when offered a blue versus a (darker) gray the animal did not go to 

 the blue at all until after three days of trials. 



The second animal also failed to discriminate red from dark grays, 

 and could not distinguish green from light grays. Yellow was discrim- 

 inated from the very lightest grays about three times out of every five 

 trials, and was readily distinguished from medium and dark grays. Green 

 was completely confused with the three lightest of the grays. This indi- 

 vidual, then, saw red and blue as dark gray, green as a light gray, and 

 yellow probably as a very light gray, though the possibility of a quali- 

 tative difference of yellow from gray could not be denied. 



The third squirrel had no trouble whatever in telling yellow from all 

 grays and white. Unless the yellow paper appeared to him even brighter 

 than white (which is possible, but seems unlikely in view of the perform- 

 ance toward green and blue) this means that the animal saw yellow as a 

 distinct quality. It was also able, after extra practice, to discriminate light 

 green from all grays, though it never learned, in 236 trials, to tell a rich 

 green from the darkest gray. It was also very difficult for this individual 

 to learn to tell blue from grays, though it finally succeeded in maintain- 

 ing an 80%-correct average on the most troublesome sequence of five 

 adjacent grays. Red was confused completely with all but a few of the 

 lightest grays, as in the other two squirrels. 



Of Sciurus vulgaris, one can apparently say about the same thing as of 

 the dog : a weak hue-discriminatory capacity may be present — ^but so very 

 weak that, within the limits of normal individual variation, it may be 

 entirely lacking in a particular individual. 



The ground-squirrels are even more certainly pure-cone than the tree 

 squirrels typified by Sciurus spp. One of them, the souslik (Citellus 

 citellus, the European counterpart of our thirteen-lined spermophile) was 

 studied by Kolosvary; but only as to color preference. When offered 

 strips of white and red paper as nesting material, the animal at first took 

 twice as many white ones as red, later became used to the red and took 

 about equal numbers of both. When white, blue, and black strips were 



