COLOR VISION IN BIRDS 501 



pupil. The pupils of four species of owls, on the other hand, contracted 

 more to blue than that of a man standing alongside of them. The pro- 

 cedure was to alternate the same two lights, respectively red and blue, on 

 the different pupils under the same adaptation conditions, watching to 

 see under which light the pupil closed the farther. Having available by 

 chance an intelligent, totally-color-blind man, Abelsdorff dimmed the 

 blue light until this subject's pupil remained unaltered during the alter- 

 nation of red and blue. Though these two lights were now equal in 

 brightness to the achromatic man, the pupil of an Athene noctua still 

 contracted farther under the blue than under the red. Similar behavior 

 on the part of the cat's pupil (in contrast to that of the dog, which 

 responds like man's) convinced Abelsdorff that the greater sensitivity to 

 blue in nocturnal birds and mammals is due to the greater concentration 

 of rods in their retinae — which also, of course, accounts for any dimin- 

 ished sensitivity to red light (such as occurs in rodents) , since the rods 

 are not stimulated by light which rhodopsin does not absorb. The lessen- 

 ed sensitivity of the pigeon to short-wave light was naturally explained 

 by Abelsdorff on the basis of oil-droplet absorption. 



Laurens in 1923, and Erhard a year later, between them confirmed 

 Abelsdorff and accounted for Piper's peculiar findings. Laurens found 

 that the pigeon does indeed have a Purkinje phenomenon, but that it 

 takes all of 45 minutes for any discernible effects of dark-adaptation to 

 manifest themselves. Piper had not waited long enough to get actual 

 dark-adaptation, and consequently missed the Purkinje phenomenon; nor 

 had he, like Laurens, used light beams of equal energy content, and he 

 therefore obtained fallacious maxima. With equalized lights, Laurens 

 found that the pupil of the light-adapted pigeon responded between 

 A704m[i, and A,424m[X, maximally at A,564mp,. Scotopically, the spectrum 

 was shortened at the red end to A,664.5m^ and the maximum was shifted 

 to A524.5m[X. All wavelengths longer than 524.5m[l were lessened in 

 effectiveness by dark-adaptation, while the shorter wavelengths had in- 

 creased pupillomotor efficacy. Comparing the pigeon with man and the 

 alligator, Laurens found that in the pigeon the maximal contraction and 

 dilatation of the pupil were carried out much faster than in man (thanks 

 to the striated iris musculature?), while the alligator's contraction-time 

 was intermediate, its dilatation-time (because of cold-bloodedness, despite 

 striated muscles?) slower than that of either man or pigeon. 



Erhard, also studying pupillary changes, found that short-wave lights 

 are brightest to owls, less bright to hawks, and least bright to fowls. This 



