788 LIGHT AND LIFE 



candescent bulb, but both were differentiated from all other wave- 

 lengths between 400 and 690 m/^. Within the red (630-690 mix) color 

 differentiation was very small; however, wavelengths in this region 

 were differentiated from all shorter wavelengths, particularly blue and 

 blue-green. Similarly, blue and green were most sharply distinguished 

 from red, least well from closely neighboring w^avelengths. 



These experiments support the interpretation that the blue-green 

 and red maxima in the spectral sensitivity function are due to the 

 presence of two different color-receptor mechanisms. The argument 

 is further bolstered by Antrum and Stumpf's finding of an anomalous 

 fly which was both color-blind and lacked the 630 m^ maximum. 



Unfortunately, the picture is not quite so clear as the preceding 

 paragraphs imply. Antrum (1) subsequently described the spectral 

 sensitivity (actually height of ERG for an equal-energy spectrum) of 

 a white-eyed mutant of Calliphora. Genetically this form differs from 

 the wild-type at a single locus, and presumably it lacks only ommo- 

 chromes, the accessory shielding pigments of the ommatidia (51). 

 White-eyed flies possessed a single maximum of sensitivity at 520 mjx 

 (again, measurements did not extend below 400 m^u.) . The white- 

 eyed flies were 10^ to 10^ times as sensitive as the wild-type, and 

 Antrum concluded that this was because in the absence of ommo- 

 chromes light which enters an ommatidium obliquely can pass 

 laterally through the eye and stimulate adjacent ommatidia. He 

 further concluded that the 630 m^ peak in the wild-type was due 

 to transmission (although perhaps multiple reflections would be more 

 likely) of long wavelengths by the granules of red shielding pigments 

 in the retinulae. He did not, however, relate this interpretation to 

 his experiments with flicker potentials, particularly to the red-eyed fly 

 that lacked the 630 m^u maxinunu. Antrum also stated that in the 

 wild-type fly the increasing prominence of the 630 m^u, maxinumi 

 with increasing intensities of stimulation is a direct consequence of 

 the "transparency" of the ommochromes to red light. He did not state, 

 however, how he reached this conclusion. 



Is THE Duplicity Theory of Vision Applicable to the 



Eyes of Insects? 



The thought has recurred numerous times that the compound eyes 

 of insects, like the eyes of vertebrates, possess two classes of receptors, 

 one functioning at low intensities but reporting no information about 

 color, the second sensitive at higher levels of illumination and sub- 



