786 LIGHT AND LIFE 



of color as studied in behavioral experiments by Daumer and others. 

 They are not necessary for the "preference" for ultraviolet light 

 exhibited in phototaxis (20) . 



The Color Vision of the Fly, Calliphora 



Although there is no behavioral evidence to show that the blow- 

 fly Calliphora has color vision, analysis of the retinal action potential 

 of this insect indicates the requisite sensory mechanisms for discrimi- 

 nation of wavelengths. As was mentioned above, the spectrum visible 

 to Calliphora extends from the near ultraviolet through the red (Fig. 

 5) . Antrum and Stumpf (2) found peaks of sensitivity at 540 and 

 630 nifi, but these authors did not extend their measurements into 

 the near ultraviolet. Later, measurements of Walter and Dodt (58, 

 59) , showed peaks of sensitivity at about 340, 507, and 630 m/x. As 

 was discussed above, the height of the ultraviolet maximum varied 

 in different preparations. Both groups of workers agree that at high 

 intensities of stimulation the 630 ni/x maximum is regularly more 

 prominent, relative to the peak in the green. There remains con- 

 fusion, however, about the position of the maximum in the green. 

 Antrum (1) reported evidence that at low intensities of stimulation 

 the peak in the green shifts to shorter wavelengths; however, such 

 a shift cannot account for the discrepancy between Antrum's data 

 and the curves of Walthei and Dodt (58, 59) . Judging by the rela- 

 tive sizes of the 630 m^u, maxima, the two curves of Walther and Dodt 

 were obtained at intensities above and below those employed by 

 Autrum and Stumpf, yet in both cases the blue-green maximum lies 

 more than 30 mjx to shorter wavelengths than where it was reported 

 by Autrum and Stumpf. 



The spectral sensitivity function of Calliphora has three peaks. 

 The relative heights of these peaks can vary, suggesting that the com- 

 pound eye of Calliphora contains three types of receptor maximally 

 sensitive in different regions of the spectrum. The experiments of 

 Autrum and Stumpf (2) with heterochromatic flicker provide in- 

 dependent evidence that between 400 and 700 m^Lt the compound eye 

 of Calliphora possesses two receptor systems for differentiating color. 

 These experiments of Autrum and Stumpf did not include the ultra- 

 violet region of the spectrum. 



According to Autrum and Stumpf, two lights of the same spectral 

 content flickered alternately elicit a ripple in the retinal action 

 I)otential when the difference in intensity is greater than 7 per cent. 

 When certain pairs of colored lights were alternately flickered, there 



